I've been exploring what difference the daggerboard makes, so I ran a few comparisons with regard to speed, turning and sailing.
First of all, here is what the "underwater" view looks like, down:
extending about 22" below the hull, it requires about 25" of water to operate fully extended. In the up position, the sits about 5 " under the hull.
Before using, you should know it floats like a rock, so be sure and tether it. I use a longer line from the daggerboard bungee to the paddle bungee; when I remove it, I can set it behind me in the cargo bay, as it tends to crowd the cockpit.
At speeds between 4.5 to 5.5 MPH, the board will cost you approximately 1/3 MPH or 8 and 6% of your speed, respectively. Not much except when distance or speed counts.
Turn radius depends on many factors, so this is not definitive for all situations. Using a modified sailing rudder (center in picture below) and Turbofins, it reduced the turn diameter
from about 28' to 23' or 16% (power-on turn started at 3 MPH). This, of course, is very helpful when sailing.
Speaking of sailing, it definitely helps you point better, more so at slower speeds. My guess is about 10 degrees better than Turbofins alone, on average. On a broad reach or downwind, it slows you down noticeably (note speed penalty above). Running side by side with another Adventure, I pulled the board and accelerated away immediately (until he saw what was happening!). Again, if it's not in its slot, it's out of the cockpit and out of the way.
One more thing -- it adds to stability, especially when sailing in gusty winds, by slowing down the heeling moment and giving you a little more time to react. I especially like that feature!