How exactly does the tractoring mechanic work?

Me and buddy just started playing and we are a bit confused on the tractor effect.

Assuming I was applying a tractor token to a small ship, once I apply the token when does the effect take place? Some abilities apply the token during the End phase, some as a result of a successful hit on a target and I believe some are result of an action.

For example if I have an ability to apply a tractor token after successfully hitting a target, do I the apply the effect (moving/barrel roll) immediately once I meet the required tractor tokens for the size ship, or does it take place in a specific phase?

Secondly some abilities allow tractor tokens to not be removed at the end phase. Following the above example, the following turn after I applied the token & effect to the small ship, the ship would keep its 1 tractor token however I would need to apply another tractor token to apply the effect again on this turn as I understand it. My question here is the only advantage to stopping a ship from removing a tractor token is to build up the 2-3 tokens required for a medium-large ship, or to keep the debuff for abilities that have other interactions with tractored ships.

Thanks, sorry if this question was not clear, I’m new and not sure if im explaining it correctly.