You know how it is, there's a lovely set of resources, buildcraft oil, water for mills or maybe an underwater cavern. Perhaps you want to build an offshore city but...
Diving to the bottom of the ocean and building up with sand is risky, there's always the temptation for one more block before you surface and then that annoying glitch where you cant seem to swim upwards and powie...your life is spread over the bottom of the ocean.
Well, if this suggestion is accepted, these worries could be over. I give you the PONTOON, simply combine a boat with scaffolding and deploy with a simple right click.
Zzap... a small piece of solid land for you to build off.
Actually, for personal aesthetic reasons I'd prefer 3 boats and 3 scaffolds to produce a 3 long structure, but as I've no idea how hard it is to code multiple block structures I've decided to keep it simple.
A nice long term use would be to form barges to transport liquids or solids long distances, again thats not quick to code and would probably overlap with other mods such as Zeppelin.