I've watched the Big rocks, Lonp Props DVs a few times. In that there is a fair big of discussion on water landings.
Using the water to land is usually to give a better line for the approach. There is quite a bit of discussion regarding the lowest speed at which the tyres. still aquaplane - between 22 and 28mph for the types in the DVD, needless to say prematurely cutting the power is said to be potentially disasterous.
When taking off water is generally not used much. Where it is it seems to be only for short, very short, periods - just the last couple of seconds. So certainly it seems to be a little unbalanced in terms of its use. From the DVDs it seems to more a 'because you can' - otherwise it would be used much more for taking off.