"compact" is one of those functions mainly for use if, say, you're booting off of a very limited system (for example, a boot floppy). It will speed up read times, yes, which can make your boot process faster. However, I'm willing to bet that your boot process is slow not because you have a slower hard drive, which would benefit from reduced hard drive access, or are booting from a floppy (correct me if I'm wrong here) but more because you're probably loading many services during the boot process. (In fact, that's almost got to be it. My slack 10 system boots in 30 seconds or less.)
What do you have starting on bootup?