I've been working on an access database recently when I noticed that the size of the file had decreased from 23MB to just 4MB when I compared it to a backup I made last week. I understand this kind of behaviour might be expected if I compacted and repaierd it, but I haven't done that in a while.
I've run comparisons on the two databases, and beside a few changes I've made this week, all the data, forms, reports, modules and queries seem to be the same. I'm wondering if this could be some kind of pointer towards iminent corruption (which has happened once before on an earlier version of the database), or if there is some other explanation.
I have one that is over 400mb in size, multiple users are in it almost all the time. When I get a chance, I'll compact it and it goes to ~100mb.
If I want to do some development, I'll save a current copy to a flash drive and work on that copy. Just by saving it in another location, it also goes to ~100mb.
You did say you made a few changes, and if you do things safely, you made changes to a non-production copy. That could be the reason for the shrinking.
-edit Choosing copy/paste to another location does not shrink it, only "save as" does this for me.