I really can’t prep for every request that comes along though. And when that request comes from the bride and groom it IS helpful to have it in your collection. I have – on occasion – downloaded a track through iTunes on my iPhone and just played it through and aux/line input.
That is why for mobile gigs I always do a prep session if possible, especially for a wedding with bride and groom and ask them about their favourites, so I can have them in my collection ….
Clearly I do that too, after all I read the Digital DJ Tips Wedding DJ Guide.
Still, as these things go, on the night itself the groom will come up to you and say “hey, I remember this song we used to play while playing in the haystack, have you got it …?” LOL.
Genres are meaningless. Quality control is everything. Develop your critical listening skills over years and decades. Don’t support the industry’s need for continual sub-division. Unity is all. Good luck!