The freeroll's player count and payout structure usually determines how I approach it.
If there are 15k players and only the top 100 get paid, I will go all-in with marginal
hands. If I try to play those
freerolls normally, I can usually make it pretty far (like top 25% or better), but as the tournament goes on, I always run into these Uber Donks that have 20x more chips than me. They're the ones that survived the all-in shove fests at the start. At that point, you have to win like 5-10 shoves in a row just to be on their level, which is very unlikely. So I usually just go all-in near the start and save myself some time. If I win the all-ins and get a decent chip stack, I will play normally. If I lose, I haven't wasted much time.
However, if the freeroll has a flat payout structure and like 3-5k players or less, I will try to play normally.