I've mostly used a single prime for years. Various 50s on a Nikon D90, 20 1.7 on m4/3rds, a Fuji X100, and a 14 2.5 on m4/3rds. A BIG difference between the 50 on the D90 and the 14 2.5, but I've found I quickly adapt to the lens with my feet.
BUT, I've recently started using more zooms, simply because my three ongoing series --lighthouses, trains, and Rock City barns -- possible shots can be limiting. If I show up with just the 14 2.5 on my OM-D, I might not be able to make it work. Distance to the subject, fences, powerlines, and all kinds of weird crap in the way means that there may only be one spot where I can make it work, or make it appealing, and that might require a 30mm lens or a 150mm lens... This was why I eventually sold my X100.