Umm, I don't really understand the question but the memory on the iPod touch is divided into 300MB for the system files and fonts etc, and the remainder is given over to all of your media (ie your music, videos and photos). However, not all of this 300MB is used and so lets say there's 50MB free. When you first jailbreak and install apps they are installed into this section and so you can see that quite quickly, the space will begin to diminish. However, 50MB of apps moved over into the media section is hardly gunna make a dent in the amount of free space and that's why there is so much memory left over.
Not sure if that answers your question but every bit of knowledge helps 😉