I use sliding glass condensation covers on my custom made tank. Personally I think they are a good idea, as they help to stop too much evaporation into the atmosphere of the room where the tank is situated (mine is in my lounge). They also trap a layer of air above the surface of the water which can act as an insulating layer, helping to reduce heat loss - particularly helpful if you have a tropical/heated tank. This is also wise if you keep Anabantoids like myself - their labyrinth (surface breathing) organ can be damaged if the air above the water surface is particularly cooler than the water temperature. There are quite a few tanks sold these days without a traditional hood/cover (e.g. many 'lifestyle' aquariums) and condensation trays are usually a good idea in these to stop fish jumping out (many fish have this habit!).
As regards the lighting - as has been mentioned, modern lighting legally has to be waterproof. I believe new legislation came into force in the last year or two, and all new equipment bought these days should be fine, so in the end it's down to your personal preference.
So I think you should have no problems using your lights without a condensation tray - although personally I'm always a little nervous about water around electrical equipment, so that is another reason why I use them!
