Question- when do you lead into a raiser?

[Etats360]

I have been think about this topic, because I don't do it as much as other players. What are the reasons to lead into someone who put in the last bet/raise on the previous betting round? I see weak players make weak leads as bluffs, and I usually raise with any two.

Do people do this with draws so they can "set the price" to draw? Lead with a monster to try and induce a raise? Get information from the opponent? Or as blocking bets with mrginal hands?

What are the main concepts/thought processes when doing this?