Yeah, every script includes main.inc.php - which then, in turn includes ubbt.inc.php - so both are loaded in every page. Doesn't matter what script you include it in.
If it's something that minor, then it shouldn't be a big deal at all. If the script you're including goes through some complex queries etc... then that load is added to every page. But if it's a simple check, it's probably nothing to worry about.