^^^Well these days it's totally irrelevant for my teaching
(my players don't use their legs!), but when I do work with able-bodied players I really like the powerstep for very wide balls (and the return of serve on a wide serve actually). I think where possible you should always look to line up the outside foot behind the ball, but when really forced wide or short of reaction time (returns) then the powerstep is a great tool to maintain good posture to recover quickly. One thing to remember, you're not hitting off the cross-over leg, you're still initiating the stroke off the outside foot, the inside foot crosses over during the push out to the ball.