Is there really any need for this if we have froyo? If so please fill me in, I just don't see the point.
*cough* TROLL *cough*
But in case you were serious, there is a need for it.
A). Some phones are quite limited on the amount of space they have. Apps are getting bigger and bigger (3D games, Flash, video chat, etc). Phones are now coming with multiple gigs available for /data, so if you have a phone with only 256mb available, you'll feel the pinch very quickly.
B). Froyo's version of apps2sd relies on the developer to allow an app to be moved, and even then, the entire app DOESN'T move - only the parts that they allow to move. So even on the SD card, an app might still take up 10s of megs. Google Earth, for example, barely moves off the internal memory at all.
C). Froyo's version of apps2sd doesn't allow you to move home apps, livewallpaper, or ANYTHING that has a widget (which is a lot of apps). Rebooting will cause widgets to disappear.