Let me give a suggestion. Assuming you're familiar with Aperture Priority and Exposure Compensation, start at zero EC at whatever aperture and ISO you desire. Take an image and observe the histogram and the shutterspeed. If you want to "move" the exposure on the histogram to the right (brighter) or left (darker), add the appropriate EC. Take another image and note both the change to the histogram and the shutterspeed. Depending on the camera model, the difference between EC in Aperture Priority is nothing more than the dials and "names" of the dials you're using to adjust the shutterspeed. The same idea applies to Shutter Priority, except EC changes the aperture.

Continuing with the example, assuming your EC adjustment in Aperture Priority is a proper exposure (no blown highlights), take your camera to a situation where the conditions are different. I just came back from a room facing East in sunlight. The first few images were away from the window where the camera decided 1/80 on the shutter was appropriate for the f/5.6 aperture and the +1 EC. When I turned toward the window, the camera responded with a shutterspeed of 1/2000. That's a heck of a lot more efficient than turning the shutter dial in manual while watching the meter in the view finder. If I turned to catch a sudden situation, I'd probably miss the shot fiddling with the camera rather than focusing and shooting.

It's really just a question of preference, need, and maybe, understanding. If you've always shot in manual, you may not feel you need to change. If you feel more comfortable in A or S priority modes, you may be unaware you're really shooting manual with each EC change because of the terms applied to the camera dials.

I have shot a ton of manual images, indoors, low light and good light using autoISO. The benefit, it will choose the lowest and is very accurate. I've used it on a d7100 and d750. Set max of 3200 on the d7100 and 6400 on the d750. I let the millions of dollars expended in r&d on a feature such as this become a tool and I'm not that much of a control freak beyond setting ss/aperture. Shooting events, its very accurate as the lighting and exposure changes. I have total control of ss and aperture which I like. When I use a speedlight, I turn it off. I do spot meter quite a bit indoors. I can prove my point with images I've taken. IF I'm not mistaken, the camera will chose an iso that may not always be available in my menu and is lower than available choices. Since I shoot a ton of events, I don't have time to make changes to my settings. Plus, when shoot action (runway models walking, I'm shooting bursts sometimes and exposure is changing) So, it works for me. shot below in brown was a joint effort by my partner who did a composite for me and the 750. The other, d7100. FYI - shot in bar, taken with the best crop sensor lens I've ever used, Nikon 17-55 2.8. I know its expensive but I bought mine used, it's metal and pro level quality. Here is another shot of a local actor with available light from a window with d7100/17-55 2.8 wide open

Never be intimidated to ask questions and just ignore those that have nothing to offer. Most of us understand what it is like to be a beginner or simply want an opinion and will not be nasty or condescending. Those that do not respond nicely usually do not last long on this forum, they either leave or are blocked by the administrator. I have found there are more people on this site willing to offer their expertise or experience than the people who are negative. Everyone can use a search engine to find information, but that information does not include the personal experience that people on this site offer.