My experience jft, differs greatly. We had a double 10lb cylinder propane locker on our last boat, but used the disp. bottles for the stern rail-mounted Magma - since the propane locker was midships and usually too much hassle to connect the hose.
We also removed the small bottles after each use. But the occasional unit developed a leak - not enough to make a loud hiss, but if placed close to your ear, there was a slight hisss. Our slipmate, who we cruised with regularly, kept his bottle attached to the Magma - said it's safer keeping the leaky bottles in open air than in his vented lazerette.
This is my approach: green Colemans on the stern rail Magma barbeque, and 20 lb. propane on deck feeding the Force 10 in the galley.
If we are going down the lake, I secure the bottle with shock cord. If the weather pipes up, I remove the bottle and put it in the footwell cockpit, as this has two 3-inch pipe scuppers going aft to the stern. If the weather is REALLY heavy, I remove the Magma off the rail.
The Colemans provide about 6-8 barbeque dinners, which is more than we typically have in a season. Running a separate line from the main propane tank would be awkward and potentially hazardous...it's really not worth it.