Aileron differential is usually needed on scale models... long-spanned planes like Cubs and Airknockers with scale barn-door ailerons need it, just as the full-scales do for the same reason, and also using rudder with the ailerons is a nifty flight "feature" just as with the full-scales for planes of that configuration.
Those types are about the only models I have flown that really need it.
For very slow-flying planes, it can be nice to have, but in unusual amounts, like all up and no down. The drag of the down-going surface can drag that side around oppositely to the command, or create a tip-stall. Both disconcerting.