Yes. CHECKPOINT only affects those transactions that have completed either COMMIT TRAN or ROLLBACK TRAN.
Resetting the identity column would be used if you wanted to start at 1 again (or whatever value you started at). Perhaps you've loaded millions of rows of data into the table, but now you want to get rid of those. So you run truncate. The seed is now at 1 again (or whatever value was used in the CREATE TABLE statement). A reason to reset it is so that you don't run out of values. Of course I'd just use bigint for the identity column if I ever thought I'd need more than int could support.