Exomizer is a compression program for Commodore and other 8-bit computers. The compressed program still runs, but it takes up less space on disk. Decompressing takes some time, but usually less time than reading more data off a 1541 disk. And unlike native packers which sometimes take all night to run, Exomizer runs on modern PCs, so it runs extremely quickly.
The space savings isn’t as much of a consideration now as it was in 1986, but being able to cram as many programs as possible on a single disk image makes access more convenient.