I do not see any drawbacks of doing so
It clutters the API unnecessarily. Why not a
scaleRotation() too?
I don't think that's an often needed functionality -- positions are mostly used as points (in absolute world coordinates) and not dimensions.
neither is it confusing I think.
It is obviously confusing because it includes both "scale" and "position" but only affects one of these properties. When even eXpl0it3r, a very experienced SFML user, asks what it can mean, what do you think that newcomers expect?
If that's really a function that you're missing, then write a global function for it. This functionality doesn't have to be part of the
sf::Transformable class.