Originally Posted by billyruffn
Nos. 2 and 7 are prohibited by the Rules. Strobes are for emergencies only .....
That's my understanding as well, but the last time we were down south we noticed quite a few boats showing strobes at anchor.. it was quite annoying quite apart from the 'legality' of it all... and they weren't 100+ footers, all of whom properly showed a red masthead lamp (though even some of those didn't really need to (show red), probably.... but I guess it's a status thing..
As to the normal nav lights, on some boats their positions and visibility may be obscured by the sails themselves.. if you're going to do a lot of night sailing you'll want to ensure that's not the case. The same goes for stern lights - hanging fenders, BBQs, outboards, liferings can all conspire to block the proper sector of those lights.
A masthead tricolour is immune to those things and can be seen farther away - but bow and stern lights are more imformative, I think...