I have a 30-amp trailer and I added an auxillary 20-amp inlet, along with a discrete run of wire feeding 20-amp GFCI outlets placed near to major items that I may want to plug in.
I use this when my main source of shore power is rather weaker than the 30-amp capacity, and/or I wish to exceed the available capacity, even at a full 30 amps. I can feed the aux inlet from a generator or from a second, separate shore power source.
I don't use this aux inlet very often, but when I need it it really saves the day. Even if my next RV has a 50 amp service, I will still add an aux inlet and power bus, just to have the option of a secondary (concurrent) power source.