There is a more important reason to keep your keel all the way down, and I can't believe no one has touched on it. Balance! By that I don't mean how tippy" it feels, I mean helm balance.
With a standard sail plan and the keel fully down, there is a slight amount of weather helm built into the rig. This is a safety measure as weather helm makes the boat want to turn to windward. So if you were to fall overboard or you tiller breaks off or something, the boat will turn into the wind and stall. Likewise, If you are close hauled in a bit too much wind, weather helm will help the boat round up to avoid a capsize when it heels too far.
When you crank the keel up (even part way) the center of lateral resistance shifts further aft of the center of effort. This causes lee helm. Lee helm is bad in most cases as it causes the boat to want to turn away from the wind. Too much lee helm can cause you to have an uncontrolled accidental gybe when sailing down wind and can cause a broach when reaching in too much wind.
I am reminded of the time when the cable broke on my clipper marine 21. I didn't want to haul it to fix it properly so I docked in shallow enough water to ground the keel, then dove to reattach with cable clamps. The jury rigged repair only allowed the keel to go down about 3/4 of the way and the result was horrible lee helm. The boat no longer pointed well and as wind speed increased, it became very difficult (sometimes impossible) to tack. In lighter air I could sometimes get caught in irons halfway through the tack. One time while attempting to beat upwind, we got hit with a strong gust that heeled us over severely. In my scramble to get to the high side, I lost the mainsheet and so could not uncleat it. I had the tiller shoved as far to lee as I could reach and the boat would not round up. We were taking water over the coaming and if I had allowed the boat to fall off at all with no way to ease the main, we would have been completely knocked down. Luckily I had cross sheeted the jib so I was able to let that go at the last possible moment to save us. I hauled the boat and put a new cable on after that.
Moral of the story: sailing with the keel part way up can be dangerous.
With a standard sail plan and the keel fully down, there is a slight amount of weather helm built into the rig. This is a safety measure as weather helm makes the boat want to turn to windward. So if you were to fall overboard or you tiller breaks off or something, the boat will turn into the wind and stall. Likewise, If you are close hauled in a bit too much wind, weather helm will help the boat round up to avoid a capsize when it heels too far.
When you crank the keel up (even part way) the center of lateral resistance shifts further aft of the center of effort. This causes lee helm. Lee helm is bad in most cases as it causes the boat to want to turn away from the wind. Too much lee helm can cause you to have an uncontrolled accidental gybe when sailing down wind and can cause a broach when reaching in too much wind.
I am reminded of the time when the cable broke on my clipper marine 21. I didn't want to haul it to fix it properly so I docked in shallow enough water to ground the keel, then dove to reattach with cable clamps. The jury rigged repair only allowed the keel to go down about 3/4 of the way and the result was horrible lee helm. The boat no longer pointed well and as wind speed increased, it became very difficult (sometimes impossible) to tack. In lighter air I could sometimes get caught in irons halfway through the tack. One time while attempting to beat upwind, we got hit with a strong gust that heeled us over severely. In my scramble to get to the high side, I lost the mainsheet and so could not uncleat it. I had the tiller shoved as far to lee as I could reach and the boat would not round up. We were taking water over the coaming and if I had allowed the boat to fall off at all with no way to ease the main, we would have been completely knocked down. Luckily I had cross sheeted the jib so I was able to let that go at the last possible moment to save us. I hauled the boat and put a new cable on after that.
Moral of the story: sailing with the keel part way up can be dangerous.