Getting an MP3 at its higest quality and smallest filesize is 'half the fun'. Its like explaining why people want to make perfect clones of game cds, instead of doing a copy-to-hdd and burn it back with a cracked .exe. Both ways work, and sure, there are the 'bragging rights' but, well. Yeah. People do it because it can be done.

Alot of people these days mix cds and have portable MP3 players with a limited media storage solution. It makes perfect sence to put some effort into getting every last drop of performance/benefits from the mp3 format.
For those people, MusicMatch might not be the best program to use as it just doesnt offer the user the full potential of MP3.

No disrespect or anything, but since you have never used LAME to encode your mp3s, you havnt heard an mp3.
A quick check at LAME's homepage tells me MM does not sport any LAME codecs out-of-the-box. You are more than likely encoding mp3s using the stock Fraunhhoweveritsspelt MP3 codec that, if youve ever done any divx ripping you will know, is as buggy as an ant farm.

A typical 6min song is approx 6-7meg. Thats a pretty 'busy' song though. (Fearfactory)
Wheras a dance/pop song is even lower. (4-5meg)
Max quality settings across the board. I dont, nor ever, skimp on quality. :)
Without a $10,000 + studio setup, the difference between the mp3 and the CD is nothing.

Check the programs out at least. EAC is the bees knees for ripping cds and you can link to LAME to encode after ripping each track to make the 1-click-mp3 ability to come back again.