Does anyone use Laravel Pennant to store user settings? For example, I have a multi-tenant app and a user can belong to multiple tenants. I want to store which tenant is currently the user's active tenant. Does that make sense or is that best left out of Pennant?

I'd advise against this. Pennant's data is really only a cache of the current state of its rules and can be purged.

For your case I'd recommend a simple foreignId on your users table such as current_tenant_id