The spinup when inserting blank media has served well for me.
1) it lets me know when my media is subpar [the drive spins down quickly after reaching the max RPM; Or I can tell from the amount of vibration whether or not I should attempt to write to the media at maximum speed].
2) it greatly decreases the time before actual writing of data occurs [the drive is already spun-up]
I assume that the spin-up is more for shortening the time required from the time you click "burn". Of course, that is only my uneducated guess. But even if that's not the reason, it works well for such.
