How to manually control processes launched on start?

Every time my Mac starts, about ~210 processes are launched, requiring about ~1000 OS Threads. With every Apple update this number increases. I've been calling MacOS X BloatOS X for a while, but is there a way to do something about it?

Some of the processes are started by root, I don't want to do much about those.

However, most of them are started by my user, and most of those are for things that I do not need or that I have explicitly disabled in system preferences (keychain, messenger...).

I guess launchd is in charge of starting all this processes, is there a way to control which are started and which ones aren't? (A configuration file somewhere?).