I found from a Pro1iaq thermostat manual
"The cooling fan delay setting will delay the fan from coming on in
cool mode and keep running after the compressor shuts off for a short
time to save energy in some systems... You can select the Cooling Fan
Delay from OFF, 15, 30, 60 or 90 seconds"
I emailed them for a little more clarification. The "keep running"
part of the engineer's reply, which is what I'm interested in, is as
"The same delay at the end of the call for cooling provides what is
known as 'free cooling' because the condensing unit is no longer
running but the evaporator is still cool and the fan can distribute
the remaining cool air through the home, also helping to prevent
moisture remaining in the duct during the off-cycle. The air and coil
are still relatively cool during this short time, preventing excess
moisture from being reintroduced into the air."
That's what I suspect: "preventing excess moisture from being
reintroduced into the air", not the opposite.