Sure - I wanted a field that could be team specific and be used when connecting to services such as github as a token identifier.

It may be that in time we want to move this out of Team into a separate model of "tokens" or something with a team having many, but I thought for now it would be ok with a team having only one such token.

Once I had settled on only having one, it made some sort of sense to make this the primary key. But that's by no means a sticking point.