Defrag slows down system

every time i use defraggler my computer comes extremly slow, it's the same no matter what computer i do it on, and even if it's done on a clear windows install

all systems are Windows XP SP3, and my file system is NTFS, i've tried both on SATA and IDE harddrives...

surely defraggler is the problem as the computers doesn't have any loading problem before using the program, aswell after a new windows install

Is that during the active defrag process, or after the defrag has completed and you've closed Defraggler?

Is that during the active defrag process, or after the defrag has completed and you've closed Defraggler?

after, i'm never using my computer while running the defrag

i would really like some feedback on this, as the problem keeps appearing nomatter what computer i use defraggler on