I have a couple years of GMing under mah belt...still doesn't feel like much but...
The pro is being in control and leading people down a great planned path. A con of that is either thinking too much or not enough. You have to give yourself enough room to roll with the punches of the characters, but you have to think enough to lead them somewhere. Sure, some GMs like a sandbox concept but even so, you can't just set the stage and expect things to run themselves.
Another tip would be to not be afraid to put on some adult pants and do some management. If someone's CS sucks for x, y and z reasons, tell them and help them out. Or if someone isn't following the rules or guidelines set by posting too infrequently or just slacking, don't be afraid to ask what's up. So many GMs get lazy or scared. I still struggle with confronting players but you have to do what's good for the game and if you can help players out by ensuring lines of communication are always open and utilized, so be it.
And remember most RPs will die or have many moments where things are slow but you need to just keep yourself and the others engaged. The more encouragement there is, the more frequent posts can come. And remember certain times of the year will be hard, like when many have finals/midterms/holidays, etc. I'd say the pro for being GM is that you get to collect a bunch of passionate people together and make some cool together. The con is that it's a struggle to keep things moving, to keep people invested and interested.
Hopefully my rambles helped? Maybe?
Probably.
