Database / SQL performance question...

Greetings,

This week, one of our group had occasion to us SQL to insert a large
number of records into a work file. It was a simple INSERT INTO FROM
WHERE... It went rather quickly.

When he was finished with those records in the work file, he then issues
a simple DELETE FROM WHERE... against his work file. The DELETE took
SUBSTANTIALLY longer than the insert. REUSEDLT isn't an issue and is
off.

It's been a while since I've played in this space, so, I'm curious as to
what, on a MI/DBMS level, is going on that would account for the
substantial time/resource difference.

Thanks

DR2