If the mast is raked too far aft, the boat will have excessive weather helm. If it is raked too far forward, the boat will have lee helm. Excess weather helm is detrimental to boat speed and pointing ability. Lee Helm is dangerous. In my opinion, for good performance the rake of the mast should be adjusted so that the boat has light weather helm in moderate winds.
Raking the mast moves the center of effort of the sail or center of balance of the boat aft. This tends to push the boat into the wind, like a weathervane. Having a little of this helps pointing, because it tends to make the boat point up more. A little "windward helm", as this is called, is also a safety feature because it turns the boat into the wind (and waves) "automatically" in puffs so the boat is less likely to take on water or capsize. Having too much rake or windward helm makes the boat tend up so much that the helmsman has to have the tiller or rudder ''way off center to keep the boat headed off enough to keep the sails full. This is REALLY SLOW, because the rudder, angled way off the centerline, acts like a big brake. If the mast isn''t raked enough, the sail tends to turn the boat to leeward. This is perhaps faster, but does not help pointng. It is also dangerous, because a puff will make the boat head off, exposing more flattened sail area to the increasing wind, and can lead to capsizing and sinking. Some boats seem to work better with more weather helm than others. Some have almost neutral helms.
Historically, strongly raked masts in the 1800''s, for example, were also connected with improved windward ability. One of the reasons for this was that stongly leaning mast enabled the forestays of the time (100% natural fiber- subject to shrinkage, stretching, and rot) to be kept tighter. The extreme rake of the masts, however, moved the center of effort of the sails so far aft that to balance the vessels, the stern section of the hull was made deeper and longer. This created more wetted surface, which slows boats down. It''s a big balancing act. Have fun adjusting your rake!