In all the aeroplanes I've flown, including big jets, it was possible to perform a controlled sideslip with no worries about the fin coming off/one wing stalling/engine(s) blowing up. That still leaves a lot of aeroplanes, I admit, but taking into account basic aerodynamics, the reality of pilot inputs and motions of the atmosphere, any 'plane must be able to withstand some element of sideslip otherwise it would come apart in normal operation. Not to mention asymmetric flight.
I'm not saying it's a good idea to top-rudder your 747 round finals into a sideslip whilst on a line check. (Tempting, though...
) It might become a useful tool in more extreme cirumstances, i.e. high and
must land, everything hanging out, still overshooting. A danger is the sheer power of most aircraft rudders and thus the need to be reasonably smooth and controlled when playing with your feet. (Which airline pilots are told to use a little as possible - for good reason.)
When an aircraft gets airborne in a crosswind, it is in a (temporary) slipping condition. When you land 'wing down' the same applies. When flying asymmetrically, the yawing moment of the engine(s) is opposed by rudder & fin loads, with some lateral control deflection if necessary (or the other way round if you want to!). These situations are tested as part of certification: at Vmca, full control deflection is probably required.