I like the feel of a boom set somewhere between the shoulders and chin.
I've had old school guys claim that forehead height was once the rule of thumb.
Any discipline that's concerned with power, formula, freestyle, slalom, goes with a high boom.
Maximum height should give the best power transfer, as it's closer to the sail's center of effort. Less power is wasted in the form of mast flexing. When your sail is on the max downhaul settings, and the COE is low and backhanded, a raised boom can enhance your leverage over the sail.
I disagree with the opinion that most speed sailors set their boom low. Looking at a few videos the boom is typically shoulder height and above. On a narrow speed board, that would seem higher than normal.
If your boom is slipping from chop bounces, you might want to spend some extra time making sure the clamp is set well.