[Putershark]

There are several reasons why this is done...
1. To make sure your prop is of the proper pitch and size for the recommended WOT range of the engine and your hull.
2. To help clean up the engine of deposits.
3. On 4 stroke engines it is needed (critical) to "burn off" all the moisture build up in in the oil and oil sump. If such moisture is left behind as the engine cools AND you do not have the correct type of Marine 4 stroke oil (and that is only a band aid). Then you could have rust starting to form inside the block and crankcase. It is very important that the oil get "above" 180 degrees to do this, and that is very hard to do with any 4 stroke outboard when running and remember, that with each intake stroke, you sucking in that much more moisture that needs to go away.

So you have to remember that unlike your truck, your outboard engine is setting in water (or worse yet salt water) and that needs to be removed from the oil. So I run mine flat out (after 5 min warm up period) for several minuets or parts of my run on each trip to make sure I only have "oil" left in my oil sump, and not a foaming mixture of water and oil that could starve the engine of the one thing that keeps it all glued together, pure oil AKA Motion Lotion

Hope this helps?
Dave