I suppose it depends upon individual needs, so it's a hard question to answer.
If your using the larger RO's and filling into the van for next day, then it's not really a burden or an high expense to do so, compared to traveling and buying water.
However, if your producing pure using a RO and using a storage tank to later transfer the water, then this may become a "space/logistical" problem for some and the option to buy their water may be more of an easier compromise.
Or you could be a lucky @#@ like dazmond and have low tds and simply use DI or double DI, but I would imagine its more cost effective to produce your own, rather than buying.