The main advantage of the 64bit version is that you can run a very large library without running out of address space.
Overall memory usage should be lower with the 32-bit version if all other things are held constant, and in theory it should perform slightly better.
One build or the other may work better on your system if you use ASIO drivers that are/aren’t 64-bit clean, or have other stuff being injected into Roon’s process space.