A dark or light background for your presentation slides? Dark backgrounds work better for very large stages, where a big bright screen takes away the attention from the speaker. In smaller meeting rooms, a light background work better.
It is very inconvenient to edit and work with 2 masters of the same presentation, it is a lot of work and you always end up with inconsistencies. Presentations with a dark background give less flexibility to work with colors, and are harder to print (there are still audiences that do this, especially when presenting to institutional investors).
So as a result, I recommend sticking to a light background for most business presentations, unless you have a very specific, high-profile event that merits the design of a custom slide deck.