None that I can think of unless you need foreign key constraints between both.
> Are JOINS slower across two files than across two tables in the same file?
I was recently debugging as slow JOIN with ATTACH'ed databases and the query plan looked the same as when both tables were in the same database. I don't think it makes any difference.
But in these situations, the solution is measuring and benchmarking for your use case.
None that I can think of unless you need foreign key constraints between both.
> Are JOINS slower across two files than across two tables in the same file?
I was recently debugging as slow JOIN with ATTACH'ed databases and the query plan looked the same as when both tables were in the same database. I don't think it makes any difference.
But in these situations, the solution is measuring and benchmarking for your use case.