Hmm....I feel a little bit left out, here.
For some strange reason, I can't get it out of my head that any app in that Tray is "running" in one way or another, and taking just a bit of my precious RAM or CPU. For this reason, every time I close out of an App, unless I am specifically planning on going right back to it, I always close them in my tray. I rarely have more than 2 or 3 apps in the tray, and it never gets over 5.
I realize it doesn't actually matter, but I guess it's just the same way I use a computer. If I am not using a program, I always close it (<cmd> + Q) because I don't like the idea of it running when not being used.
I guess I'm alone in this thought process?
I'm not sure how a Mac works, On a PC of course, which like a Mac, and even going back as far as the good old Amiga, does really multitask, on a PC I may run Photoshop and Chrome and other programs and minimise them down to the taskbar as I want to use them later, but they are still there taking up memory, but not really talking up and CPU power as they are just sitting waiting for me. Of course, they could be running like Handbrake, and taking up my CPU power in the background.
Like you on your Mac, I close down programs I'm not going to want to run for a while as there's no point in leaving them running and using system resources. As I have 8GB of memory, or course, I can be less worried about this