Just look at the project, do some researches by yourself and you will understand is it worth to join their bounty or not.
Have a look at: idea, team, advisors, soft/hardcap and manager who leads the campaign. That will be enough to decide.

yup, but i personally if theres to many bounty i will do some research before participate, thats will makes my time more efective, but sometimes i do all bounty that fix for me without any deep reseach