Converting music files to AAC in iTunes?

[Dansta]

what does this actually do?
ive found that all the music ive actually copied from cd's i own are automatically converted, but others are not.

i know it makes the files smaller, so ill be able to get more on my pod, but at what expense?

thanks...

 

[iPap]

Quality!

 

[Dansta]

whats the lossless progrma thingy all about?