I think focus helps, as your set list is less scattergun in approach and that makes choosing songs easier. I’ve played in bands where the set list contained a good number of pub favourites. However, the band I had the most fun in was specifically an ‘80s covers band. This helped with choosing the numbers, on stage appearance and having a specific product to tout to venues and punters. I joined a mod band earlier this year, after moving house (not normally my kind of thing, but I was desperate for a gig) and the same advantages seem to hold for this project too.
FWIW my old ‘80s band did a good number of functions as the clients wanted our specific product.