Cutting off your control authority at the worst possible time would definitely be the risk trade-off!
When untying it only cuts once in a while when doing the bow lines and I'm still attached at the stern, so no risk there.
When preparing to dock it's only if I need to find and prepare extra rope from some of the most aft compartments, which I do well ahead of when I need them and not during "critical phases of operation".
If I expect to be running around a lot during docking I take the FOB off and place it on the dashboard. I don't leave the helm unless the gear is in neutral, and if I fall in the water I'm usually within 20 meters of land which I'm fairly certain I'd be able to reach :)