WHY THE FUCK WOULD YOU TAKE A SCREENSHOT OF A FILE YOU ALREADY HAVE!?
It's NOT easier, it is in fact a pain in the ass to extract a certain thing for a screenshot! If you have an image with a table, and an image with a lamp, and you want to make it so you have a table with a lamp on it you don't have to take a screenshot of anything. You just take the lamp and put it on the goddamn table.
Also, the layers are there for a GOOD REASON. If you want to shove a bunch of shit on one layer you better goddamn know what you're doing. Doing that before you're good with it is like all those idiots who turn to scripts for every little problem because they haven't really learned how to use the program yet.