Optimization can be interesting if you intend to invest in the sails or rigging, or the underwater body. It is important to know beforehand which option gives the best gain per euro i.e how much you will gain on speed and/or handling and what the costs will be.
Racing
Alterations to the keel and rigging will always cause changes to the performance of a yacht. Most often you want to shift performance. Get her beter running and loosing some on tacking. Racing means better speed against handicap. If we make the yacht 3% slower with a 5% better handicap, she is a much better racer!
Cruising
Optimization to a cruiser often means more speed, better handling or more comfort. In my vpp I can get optimum figures at a restricted heel angle and I can add extra windage. I might advise a less efficient, but easier to handle light air sail with a bigger range.
Common optimizations:
New keel
New rigging
New sails
From fully crewed to shorthanded
