It's a lossless codec. What goes in, comes out. This results in larger files than lossy codecs like AAC and MP3, but smaller files than completely uncompressed formats like AIFF and WAV.
Going from AAC/MP3 to Apple Lossless will not result in quality going up. You need the original CD or vinyl source to rip from.
I have 16000 tunes. I own 12000 of them, all ripped from the original CDs/vinyl. I don't buy downloads, and will not until lossless files are widely available to purchase. Even then, I'll only buy something if it's ONLY available as a lossless download. If there's a CD, I'll grab that.
It depends what you spend your money on. Some people spend it on movies, some on baseball cards...I spend it on music and musical instruments.