VHF radios that conform to the ETU spec have two power settings 1 or 25 watts for fixed sets and 1 or 5/6 watts for handhelds. If you were calling for help especially in a MAYDAY situation you would naturally choose high power so that the Coastguard and as many vessels as possible would here your call.
But using high power for routine calling severely restricts the number of people who can use the few channels available at any one time – in other words several 1 watt conversations can take place within a given area but only one 25 watt conversation. Misuse of the high power setting is a bit like walking into a bar and shouting at your friends – eventually everyone will have to do the same and that is counter productive.
Marinas can only reply on 1 watt if they comply with their license, race management uses channels M and M2, and inter ship is channels 6,8,72 and 77 – so it is a good idea to use the right channel and use only low power – that means you should only be using high power on channel 16 – Coastguard.