jerryc41 Loc: Catskill Mts of NY

I save that for post processing.

dpullum Loc: Tampa Florida

DEFINITIVE STATEMENT: I paid for every sq mm of that sensor why would I not use it; like Jerry, I crop post processing. Crop in camera and then look at large on-screen image and yikes you just missed something that would "make the image"... bad news. Get as much real estate as possible, then crop with edit. Of course, here in USA we are often like me, tied to typing paper size dictated by paper size. Paper size is a whole nother game!! and indeed if we are going to print at home most of us use an 8x10 printer; I do.
Education one's self is important to understanding our photography... but is it necessary to understand photography [and aspect ratio] do great photography... No, I do not think so.

WHAT EVERY PHOTOGRAPHER NEEDS TO KNOW: The American/Canada/Philippine standard 8.5x11 is determined originally by 1/4 of the manually made paper makers arm... rational, huh. " a quarter of "the average maximum stretch of an experienced vatman's arms." My guess on the 8.5 is that spread thum to pinky tip is my quick 9"measure [may change Trumps ... fingers are small and as our President brags is not an indicator of his personal parts !! True quote !!] So when printing for home display I use my 8x10 printing. Aspect ratio of roughly 1::1.3. [FF sensors are 1::1.5] Our USA standard paper is indeed one quarter of the old Imperial paper size known as Demy, which was tied to the dimensions of the King of England who's thumb is an imperial inch. Thes are important things to know if you hope to be a great photographer. Great fodder for group discussions. ??WHY DO WE CLING TO BRITISH MEASUREMENTS LONG AFTER THEY HAVE ABANDON THEM?? Well, We and Zimbobway; rest of the world is metric.
https://en.wikipedia.org/wiki/Paper_size

Back to camera sensor sizes and aspect ratio: This link has links to additional information on the aspect ratio of various sensors. http://www.shortcourses.com/sensors/sensors1-5.html
A detailed short course, 18 pages, of information on Pixels and Images and contains information on aspect ratios. http://www.photocourse.com/itext/pixels/pixels.pdf

Delderby Loc: Derby UK

Having been M43 since the beginning of the mk, I have grown to prefer (and appreciate) 4:3, although I could easily change this "in camera". If I zoom or crop during PP, I usually maintain aspect ratio. However, when printing - usually 7x5 or 6x4 (which I think is "comfort size" for photo books) - I am forced to alter things a bit. I have seen some great landscapes printed square, as well as 3x2, and also 4x3. I have a project which involves shooting landscapes without sky, which surprisingly, seems to work better in 4:3 than 3:2 - without a sky a horizon is not necessary, but foreground becomes important. My other project is to produce 6x4.5 photo books. My regret is that I cannot print two pics from one A4 sheet.

johneccles Loc: Leyland UK

I have recently changed my aspect to 16:9 on both my cameras, I know that the MB resolution is reduced but I view all my photographs in 16:9 screens so the images look much better.

Architect1776 Loc: In my mind

I crop the photo as needed to look right. I don't care about aspect ratio but how it looks, then when framing make the mat the correct size.

camerapapi Loc: Miami, Fl.

My Nikon bodies are shot at a ratio of 3:2. My Olympus at 4:3.
Things only change in post if I am going to enlarge the file.

BlueMorel Loc: Southwest Michigan

My camera shoots 3:2 but my in my post i crop whatever aspect looks pleasing to me. I rarely print, so that usually doesn't enter in.

par4fore Loc: Bay Shore N.Y.

Fun to shoot in camera 1:1 square format to mimic film (6x6). This can help and be fun when you are in a creative rut.

Jack 13088 Loc: Central NY

Your physical sensor (film) has an aspect ratio of 3:2 so if you ultimately want a different ratio on print or paper you discard some of the available pixels. So why do that in the camera? Do it on your computer where you still can have a do over.

The trick is to NOT tightly crop in the view finder. You probably have way too many pixels available in your camera. Give yourself a margin before you press the button. I have been trying to teach myself to do that for say 50 years! Maybe some day. The introduction of zoom lenses did not help. Wedding photogs that shoot 2 1/4 x 2 1/4 have mastered that trick.

DavidPine Loc: Fredericksburg, TX

Post is where you should be more concerned with the aspect ratio of your image. Is it destined for instagram 1:1. You mentioned 8.5 x 11. You can make it that size or use 4:5 and be happy.

rmalarz Loc: Tempe, Arizona

No. Probably a carryover from using film. I might change in processing, but not in the camera.
--Bob

Longshadow Loc: Audubon, PA, United States

wrangler5 Loc: Missouri

I make photo books for the family (extended) at Christmas, which total about 1,000 prints, all of 'em 8x8 black and white. One of the most appreciated features of the M4/3 cameras I switched to last year (after almost 50 years with mostly Nikon cameras and lenses) is the ability to set a 1:1 aspect ratio and monochrome for the composition. I shoot all RAW files, which include the full frame and color so it's all there when I start my processing, but for composition I no longer have to guess what will or won't be in a square frame.

jeep_daddy Loc: Prescott AZ

The only time I change aspect ratios is when I'm specifically going to post to Instagram, or if I'm going to use the photos on Craigslist or eBay as ad photos. I usually change to 1:1 size for this purpose. Otherwise, I just keep the aspect ratio at 3:2.

DebAnn Loc: Toronto

It's never occurred to me to change the aspect ratio in-camera. I choose between horizontal and vertical when shooting, then crop however I like in post.