This excerpt from a mast/sail design manual may better elaborate.....

• Sail Shape & Boatspeed — There are several reasons to use prebend. The main benefit of prebend is to
“match” the mast to the luff curve of your mainsail. If the prebend and luff curve are in sync, then the mast/sail combination will have a wider wind range potential. Net net is more speed. Another benefit of prebend is a more stable mast.

The most important use of prebend is to match your mast to your mainsail. If you sail in a class that has an optimum rake and prebend, your sailmaker will construct a mainsail with a luff curve and an overall design to match this mast curve. If a main is built with too much luff curve, the sail will be too full in medium- to heavy-air conditions and cannot be depowered. Assuming your mainsail is built with the proper luff curve to optimize the speed and versatility of the sail, your prebend should be adjusted to best match the sail. For instance, if the lower portion of the main is too flat in medium air, try reducing prebend by any of the methods discussed earlier. Working closely with your sailmaker to “match” the sail and mast bend will mean more speed on the
racecourse. To have consistently good boatspeed through a wide wind range, you must shift gears to change sail shapes to suit the wind and wave conditions. If your sail and mast are in sync, the sail shape transition is almost automatic simply with downhaul/outhaul tension. If your sail and mast are not in concert, you will grind your way
through the wind range with less boatspeed. Bottom line: spend time getting your prebend right. The results are dramatic on the racecourse.

Sail fast, Tom G