How often do you use/need a 50 amp to 30 amp adapter?

I almost always use the 50 amp, they are in better condition, usually.
Where we stayed this past weekend there were 50's but no 30 amps, so yes I use it.
I had a 50 amp put in at my house, where I store the trailer and use it all the time. It didn't cost me much more than putting in a 30 and if someone visits needing 50 amp, or we get a bigger unit, we are already set.