I allow 3PP material and homebrew material. I'm actually running an adventure path that had a companion book full of player options (new archetypes and such), and I asked everyone to choose one of those archetypes (getting my money's worth from that kickstarter).
In my normal game, I allow WotC published material pretty much as is. I allow UA with the caveat that if there are balance issues, we adjust as we go and if the material is released in a full product then you shift your character to the complete version.
For 3PP and homebrew, I look it over and approve it first. Certain publishers have more credibility to me so their content passes a little easier. This step does take time though because I usually have to reference a bunch of other material to see how it stacks up. If its homebrew, I usually ask for a link to a reddit or forum post where the material was discussed. That's an easy way for me to see concerns others had and reasoning behind design choices. The Unearthed Arcana reddit and ENworld's homebrew forum are both good sources for that kind of discussion.
The biggest reason why is that I know some people like to play something new or different. Some people have a something particular that they want their character to do or be that the core rules cannot fully accommodate or requires such a large degree of multi classing that they don't get to be what they want until high level and are probably underpowered if they make it that far.
An individual bonus for me is that allowing 3PP/homebrew material has increased my own level of system mastery. Evaluating archetypes, classes, spells, etc... forces me to dig into the classes and try to figure out the rough balance levels. It helps you drill down to really get a solid hold on the action economy and resource management.
In my normal game, I allow WotC published material pretty much as is. I allow UA with the caveat that if there are balance issues, we adjust as we go and if the material is released in a full product then you shift your character to the complete version.
For 3PP and homebrew, I look it over and approve it first. Certain publishers have more credibility to me so their content passes a little easier. This step does take time though because I usually have to reference a bunch of other material to see how it stacks up. If its homebrew, I usually ask for a link to a reddit or forum post where the material was discussed. That's an easy way for me to see concerns others had and reasoning behind design choices. The Unearthed Arcana reddit and ENworld's homebrew forum are both good sources for that kind of discussion.
The biggest reason why is that I know some people like to play something new or different. Some people have a something particular that they want their character to do or be that the core rules cannot fully accommodate or requires such a large degree of multi classing that they don't get to be what they want until high level and are probably underpowered if they make it that far.
An individual bonus for me is that allowing 3PP/homebrew material has increased my own level of system mastery. Evaluating archetypes, classes, spells, etc... forces me to dig into the classes and try to figure out the rough balance levels. It helps you drill down to really get a solid hold on the action economy and resource management.