Excellent Lighting is a must for the younger generations, for the middle aged it's purely a bonus and for the 50+ they are possibly indifferent

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I find that to some degree Scans annoy your audience especially at more formal social gatherings, to the point where I no longer use them at weddings, unless the larger functions.
"Non Scanning" effects are easier to control, when you point them at a dancefloor, wall or ceiling they stay put. Scans on the other hand, by default are likely to scan at least 180 degrees i.e the entire width of the room, and also move up and down. This means that wherever seated, your audience are, at some point, going to get blinded. With modern optics and 150W discharge , 250W Halogen and 575W Metal Halide lamps, this can be extremely annoying to your audience, who can't look at the person across the table at them for your Scans randomly hitting them right in the eye without warning!.
If you do a lot of Teenagers Disco's, Clubs, 18th's etc then you are likely to reap the benefits, if like me, the majority of your functions are Weddings, 40ths etc, then consider the cost, along with the potential to lose work because you are annoying your audience.
Like Sound I carefully make sure that I aim all my lighting into the area of the dancefloor. This leaves a quiet, darker area for the older generation, or people not interested in the disco to sit and talk, without too much inconvenience.