Image compression Vs. not compressing

[Quitch]

The help file doesn't seem to offer any explanation as to what image compression does. Okay, it's going to make the file smaller, but what are the pros and cons? What's a rule of thumb space ratio? Will I be seeing meaningfully longer load times? etc.

I see a box but I don't feel the program gives me the information necessary to make an informed choice.

[Blazkowicz]

I haven't seen any longer load times and on one image it already saved me 2 GB.

[Quitch]

Not sure someone who delivers information using a Kane avatar is to be trusted though

[flipside5]

I'm resurrecting this old thread because I'd like to know whether the compression is lossless. When making a copy of a movie, if I click the compression box, will the quality of the movie be reduced?

[Terramex]

Quality won't be reduced.
But as movies usually are already heavily compressed don't expect too much space-saving.