Compressing your backups has very few downsides. It’s usually faster (the additional time for compression is less than the time saved by reduced IO) and of course, the backups are smaller. I have run into a few issues, however.
On one occasion there was 75gb free on a drive, the last full backup was only 50gb and the database had not grown significantly in size. Interestingly there was an error when we tried to run a backup. Not enough disk space.
Read on for the explanation as well as the solution.