Pay is not that great.
They don't provide benefits. You have to find all your own and then you get reimbursed. But that can have hiccups
They can skimp out on mileage reimbursements.
Communication is ridiculously poor.
When a project is over you are left in the dark until a new one starts, but you have no idea how long you will be waiting (as in potentially weeks)
It's VERY hard to transition from part time to full time, and full time is only 30 hours guaranteed.
Gaining new skills can be hard you have to be hoping that everyone else is busy and you are the only person left to do something because work can get scarce so people understandably don't want to share what they know or what they are doing or else they might lose hours.
You basically need to buddy up to someone in management so they can get you more hours, if you aren't the type of person that wants to be friends with your manager, it's next to impossible to be one of the people who gets work during the slow periods.
