The subtle Caffeine menu bar item is built for one thing in specific: keeping your Mac from going to sleep. It comes in handy if you want to be able to use your Mac whenever, without waiting for it to come out of sleep or hibernation or of putting up a screensaver.
I wouldn't overuse Caffeine though, because sleep and screensavers are there for a reason, that is conserving your computer's energy, and also making better use of the battery. If you keep your Mac always on and active, you are using more energy without giving your Mac a rest.
If you need to keep your Mac awake though, it's very easy with Caffeine. You activate it by clicking on the menu bar item. If you keep the Command key pressed at the same time you'll bring the program menu.
Caffeine keeps your Mac awake. Just don't overuse it otherwise it might get edgy.
Fixed a bug where Caffeine was effective when another user account was active
Very quick to activate
May use up a lot of your resources
"Rgee no sleep with Caffeine"
I like Caffeine, it is simple to use and does what it is supposed to do, keep my computer awake, I do a lot of reading and video watching and to save changing preferences it is much more simple to just click on the Caffeine icon in the menu bar to prevent the Screensaver cutting in and having to login again. I use it quite often as I have my Screensaver set to go in 15mins.