anotherview Loc: California

I've decided that seeking a wide aperture like f/1.4 (and even f/2.8), and so on, involves a fetish. Such apertures go with a specialty lens for a limited purpose. Most all photography takes place at smaller apertures.

If more light becomes needed, then turning to artificial lighting may provide the best result for the exposure.

Peterfiore Loc: Where DR goes south

As we all know, It's so very true.

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

You do not need a fast lens for a snow flake, in fact, it you want to use a macro lens to capture the snow flake, stopping down your lens to say f8, f11, or f16, you depth of field increases so that snow flake taken at f1.8 may be sharp in front, but not in back, at f16, you snow flake might be sharp all the way through, make sure to focus on the front as depth of field increases as the subject moves away from the camera.
Also, the big advantage of a FAST lens is that you can isolate your subject, it also becomes HARDER to control over all sharpness because of your limited because of a shallow depth of field.
You will have to be very aware of what is in focus when shooting wide open.
But, wide open can isolate your subject, below is an example taken with a 600mm wide open at f4, notice how the Red Shoulder Hawk seems to pop out of the smooth creamy background.
Again, focusing wide open even with a 1.8 lens can isolate your subject, but be mindful of what's in focus.
Good luck and keep on shooting until the end.

BebuLamar

You missed the bragging right!

SuperflyTNT Loc: Manassas VA

You want this guy’s setup to take photos of snowflakes
https://www.uglyhedgehog.com/t-683481-1.html

RWR Loc: La Mesa, CA

Rather than copying what others here recommend, I encourage you to think for yourself.

jerryc41 Loc: Catskill Mts of NY

Basically, the faster the lens, the more light it is able to admit. However, along with more light comes larger size, more weight, higher price, and, possibly, a decrease in image quality.

Kmgw9v Loc: Miami, Florida

I don’t agree that owning 1.4 and even 2.8 aperture lenses is a fetish.

DirtFarmer Loc: Escaped from the NYC area, back to MA

Responding to the title of the post:
I would not expect any one person to come up with ALL the advantages of fast lenses. The responses have pointed out some of them, and many have limited their response to the text from the OP.

One more "advantage" is that faster lenses, since they have large elements, are heavier. That will reduce camera shake from mirror slap, shutter action, or essential tremor (to name only a few sources of lens disturbances).

clickety

Fast lens? Things I didn’t see in comments:
Usually will have better optics
Usually will let you spend a lot more money
Usually will add considerably more weight
Usually will look more impressive

User ID

You’re recommending quitting the UHH ?

User ID

Do you mean in the real world, or online, or at your camera club, or ... ???

RWR Loc: La Mesa, CA

Not really. This kind of nonsense keeps UHH going!

reverand

As others have noted, the main benefit of a fast lens is shallow depth of field, so you can get nice bokeh if you're shooting images where you want only a shallow field to be sharp, i.e., when you're photographing, say, a flower, and you only want a few petals to be sharp. And the main advantage of a fast lens used to be speed, especially important to journalists working in low-light situations.

Barring that, there are few advantages to a fast lens, especially since today's cameras can produce good images at high ISO's--in other words, in low-light situations, you no longer need a fast lens. Your camera can do the work. It used to be that journalists who used Tri-X at ASA 400 might "push" Tri-X to 800, or even higher. My Nikon D850 works well at ISO 1600--I only start noticing noise at ISO 3200, and it's actually not much noise at all, compared to pushed Tri-X.

A fast lens also costs more, it's heavier (especially in telephotos), and its aperture for maximum sharpness is likely to be f/4 or f/5.6, whereas a slower lens is going to be sharpest at f/8. I generally try to shoot my landscape work at f/8 to f/11. For macro work, it would seem to me that a slower lens, at a smaller aperture, would be preferable.

Miami39 Loc: Florida

If you take portraits or street photography, fast lenses tend to give better bokeh. I have a Nikon 85 f1.4D that really blows out the background when shot wide open or up to f 2.8. I like the effect. You have to be careful as the depth of field wide open is very shallow and isolates the subject from the background. One of the other posters noted that a lens may not be as sharp wide open but I have not had that issue.