Is the swap there for some specific purpose or "just in case"?

By default N9 has 256 MB of ramzswap (compcache) configured and it uses no actual swap partition or file on MMC. The swap device is /dev/ramzswap0 and can be seen with 'swapon -s' command (-s needs swapon binary from debian). It can be turned off with command /sbin/swapoff /dev/ramzswap0 in 'opensh' or when you are using 'open mode'.

I've been running my N9 now for a week without, and haven't noticed any negative effects (yet), even under heavy multitasking and memory usage situations. The 1 GB amount of RAM seems to be enough for pretty much anything.

Since ramzswap uses cpu when swapping, it might have slight smoothness increase depending on the situation and different usage scenarios.
For the record the reason I disabled it was to get rid of the irritating lagginess which happens every now and then when typing in the security code immediately after the phone wakes up from the sleep. It seems to have helped with that at least...