Chasing should mainly be determined by the pot odds. You need about 5:1 vs bet in the pot on the turn/river to call. In general, chasing out-of-position or with few opps (1 or 2) is unhealthy. Now if you have a flush draw with 2-overcards or a pair, you hand is much stronger... Assuming your overcards can be considered as outs. In these situations your about a 50/50 on the results.

If the bets are overly large (say 50ish% of your stack) and you have pot odds, you still might want to consider folding. Competing will open you up to bigger wins (33% of the time) and big losses (67%) of the time. I like chasing if I know the betting is going to be fairly "normal" (no loose/aggressives in the pot). Its low risk / high reward versus high risk / high reward. From what I found you always want to be in the best risk/reward situations. E.g. loose/passive, tight/passive, tight/aggressive. In my opinion loose/agressive styles are the hardest to play against in a ring environment