When should you pin the knights on c6 and f6?

Most of the time when i am looking at analysis it has a love/hate relationship with pinning the knights guarding your center. As a 1200 i am not sure why these types of moves would benefit you in the opening. Maybe Someone could give me examples of when the knights should be pinned and when they should be left alone.

Many lines of the Caro Kann involve pinning the knight on f3 with the bishop. This is because the knight is specifically defending the two white pawns placed on e5 and (usually) d4.

A pin should serve a purpose, either because you specifically want to capture that piece (it can't move out of the way due to the pin), you want to attack what it's defending, or you want to otherwise limit the moves your opponent can make in response.

In a number of situations, the early game pin is the only active square for the bishop, and you play it for lack of anything better as you develop.  Some players take the knight, trying to create a pawn structure problem for their opponent.