A lot of laptops nowadays are smaller than a TKL, at least mine is, so a 60% board makes sense.
Also, a 60% is the same as a full size board for most typing, everything is in the same place, including numbers and symbols. When you have to really reach for other keys (F-keys) or move your hand position (Arrows, edit and numpad) you may as well use a layer and keep your home row position (F-keys on top row, embedded numpad on right, edit and arrows on left perhaps), so 60% is ideal, IMO.
I am starting to like smaller and smaller boards and would love to try a 40%, but I suspect it will be a little too much work on the function layers to be really productive for me, although I love using my 48-key ergo board, so who knows?
As an aside, although I am very used to the normal arrows and edits area on a full size or TKL, I quite like the idea of using ESDF as arrows, W as home, R as end, T as PgUp, G as PgDn, maybe A as del on a 60%.