Basics: Mostly, the only people who Town Hall snipe are Town Hall 6-7 since they lack the troops to push in any other way. From one Town Hall snipe you get between 4-11 trophies depending on difficulty (A revenge raid can get you more or less). Usually if you want to Town Hall snipe for trophies, then you want to have mostly archers/ barbarians plus a couple giants in case hidden teslas spring out. I would recommend (for 180 troops space) bringing 10 giants, 80 archers, and 50 barbarians. If you want to be a farmer, then simply put your Town Hall outside your walls and fill in the hole it left.
The Good: There is actually many good reasons for TH sniping. Its a win-win situation for the snipers and the snipee. The sniper gets those trophies while the snipee gets that free 12 hour shield. TH sniping is also a very easy way to get to crystal, even if it isn’t very well respected. Also if you are a farmer and you keep losing attacks since the loot matters more, then you can snipe some Town Halls to get back up where you need to be.
The Bad: There aren’t too many bad things about Town Hall sniping (if you don’t agree, look down in the ugly section ;)). The only way it can go bad is if a snipee put teslas and heroes around his Town Hall and you didn’t bring enough troops to take out the teslas and heroes along with the Town Hall. Also be careful who you raid! Some high level players you snipe will take revenge on you and get up to 59 trophies on you! Watch out who you raid! Example: http://www.youtube.com/watch?v=9XQElHtu1BA (Skip to 3:00)
The Ugly: Many, and I mean MANY, players resent Town Hall snipers because they say snipers have no skill in the game and require trophies handed to them. If you go out on global as an XP 30-50 and crystal, be ready for some hate from high level players. If getting to crystal is bad enough by sniping, then master is awful. You will be banned from global if you are too low level!