Space loss/gain after defraggs?

I defragg when I notice the slightest decrease in speed during off hours(when internet is least busy). I always check free space count just before and right after.

Strange.... sometimes I gain(as much as 2GB) and sometimes I lose(always 1GB); and sometimes I neither gain nor lose. And stranger still.... between defraggs, I notice I might gain back some lost space or lose some gained space hovering (back and forth) at 258 - 259 free space/298 total (86-87%).

Why the loss/gain variation in free space right after defraggs?
I think I can understand losing space.. but not gaining, between defraggs.

(During this 5 weeks of observation, I have not changed/modified my system....nothing to tweak So, this space gain/loss is really baffling me)

Hi CoolNewYorker,

Since it is only 1 to 2 GB, then this may just be space used by the pagefile on your hard drive that is being adjusted as needed. I would not worry about it unless it gets to much beyond that amount.