If the self-propelled mowers were not designed to be used that way,
it would be pretty stupid, because that's how they have to be used in most
applications.
Almost eveyone has areas, under trees for example, where you need to
do this.

While a self power mower might seem like a good idea, I think a much better
one is to get a lighter mower.

I had an old lawnboy, all plastic, that lasted years and was MUCH lighter
than any other mower I've ever had. Wish I could find another.