Confused about Compressed option in Disk Utility?
When you create an image and you select Compressed, you are doing so at the sake of speed and read/write capability

To access the data on a compressed image, you have to uncompress it first; that takes cycles (cpu time).  Secondly, per Apple, the image is read only, not read/write so you will lose that capability as well.

The "Compressed" format is great for archival of data, not for daily access.