Re: Start eng. in gear??
Several people I know do it for exactly that reason. For "overpowered" boats especially I've been told it is really important not to shift into gear at any higher rpm than necessary. Shifting at higher rpm provides a greater risk of chipping a gear toloth... which can then lead to catastrophic failure under heavy throttle.
The problem with this is obviously that you don't have reverse, etc, etc, etc... and that you either launch from a very uncrowded ramp or dock, etc...
I would think this is really only marginally convenient / reasonable option for an extended period of time on a boat you never use for what most would consider typical pleasure boating (as in running hard offshore where an engine build more like a circle track car rather than a typical marine engine might be the ticket).
Finally, unless trying to wring every last pony out of an engine, modern cam profiles don't have to give up nearly as much power to give a reasonable idle as did those available even 10 or 15 years ago.