In a single make class weight saving is one area where you can differentiate one bike from the others. All you have to do is take stuff off!!! - its easy
It'll really help getting the bike off the line and out of corners.
Saying that, it was probably my third year in DD when the bike had been stripped down completely and rebuilt that I weighted any part that went on the bike.
Just consider every part of the bike and see if any parts can be easily removed or swapped for lighter items. On my DD620, I managed to shave around 16KG of weight (2.5 stone!!!!) off by going through this process.
The major savings would be exhaust, swingarm, disk/caliper and battery too, but it all adds up and you need to consider every mount and bolt. Do you really need that hugger? Chain guard? crash bungs? Battery box? Heavy exhaust mounts? Use cable ties where bolts/brackets are not necessary.
Tim