In general the Hollywood unions are very good for their members.
If there's a downside, it's that they used to act as a bit of a moat for the incumbent studios. Studios have entire departments devoted to processing issues raised by union members, which is of course expensive to do. And union members can only work on union productions, which meant tiny indie films could have problems getting talented people budget-wise. It's not just pay, it's meeting the requirements of the dictionary-sized "Basic Agreement" in terms of other aspects of production. That said, SAG has led the way to finding ways to accommodate smaller budgets and it's not as difficult as it once was.
If there's a downside, it's that they used to act as a bit of a moat for the incumbent studios. Studios have entire departments devoted to processing issues raised by union members, which is of course expensive to do. And union members can only work on union productions, which meant tiny indie films could have problems getting talented people budget-wise. It's not just pay, it's meeting the requirements of the dictionary-sized "Basic Agreement" in terms of other aspects of production. That said, SAG has led the way to finding ways to accommodate smaller budgets and it's not as difficult as it once was.