Newb questions:
When is the best time to farm mercenaries, and are there certain classes that should always/never do this?
Are all of the abilities that boost minion/mercs traps?
I'm glad this topic came up, because I was going to post on it myself.
Here's the advice I would give:
* Mercs are objectives. If there's a teamfight threatening to happen, or the enemy is anywhere near you, don't take them.
* The boss is a big objective, so if the enemy team has five players on the map, you should really just never do boss. Even apart from getting jumped, it's going to take a ton of time that the enemy can use to push buildings and clear other camps.
* A good time to take mercs is when you have a temporary manpower advantage because you just won a teamfight. Contrariwise, a really stupid time to take mercs is when you are down players.
* Just because your hero can solo merc camps doesn't mean you should. If you are soloing a camp it means the rest of your team is doing something else. Why aren't you doing that thing instead?
* Bruiser mercs, in my experience, slightly help push a lane but don't really win games. Siege mercs can easily clear buildings, but they're easy to kill.
* Early game, mercs are not more valuable than soaking an empty lane. Late game, mercs are not more valuable than map objectives.