An ADF doesn't have to be 880K, but at the same time you need to fully know the contents of a disk before you start trimming.
1). Any ADF that has an AmigaDOS filesystem CANNOT be trimmed down under any circumstances!
AmigaDos writes file data all over a disk, a block here, a block there. Do not do it!
2). Any trackloading game CAN be done, as long as you know that the end of the disk is empty.
For instance, Stunt Car Racer is a 1 disk 880K ADF, if its a duplicate of the original (and patched cracked) then you can trim it down to 490k, because the other half of the disk is empty.
Frankly, unless you know a great deal about the Amiga and know what to look for in an ADF as data or just junk, I would leave well alone. Hardly seems worth bothering with a few K when 20 Gig drives are cheap as chips!