it's a (misguided, if you ask me) PPRuNe policy to prevent kids from getting the idea to shine those devices towards aircraft cockpits for fun. This way the thread doesn't show up when you do a Google search.
Its illegal and potentially dangerous to not just flight, but the eyes too; something I know some police constabularies are very hot on.
As for estimating the cloud base... no idea. For me a game of 'met-man says'. If its within limits go see for real, if not sit on the ground until it is. At least if I crash it the AAIB can rule out that I weren't qualified to fly in the weather conditions at the time.