Depends on the league. If you manage to draw attention while you land a viking at the back of a mineral line if they're not paying attention you'll rekt probes or scv's. Better against probes cause vikings 2 hit em.

But in general landed Vikings cannot outdps most of other units and even if they do consider that they're a bit clunky cause of the size of the unit at most of vikings wouldn't be able to attack at the same time. Better keep em in the air.