We do have significant currents (large tides) and I have to say I hate it when someone blocks my line of sight to the knotmeter. For me the through-the-water speed is crucial feedback/data for steering and sailtrim, as much as telltales and waves.
Also since our GPS is a handheld on the pedestal, the knotmeter is a much easier-to-see instrument with a larger readout, esp when steering from the rail.
Still, even though I've done it dozens of times, the old 'swap the plug' in and out always makes me nervous!
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)