Very well said Bearpaw - pretty much 100% hits my reasons for going solo.

As for the "partial partners" I do this with a very few people, and in select locations, only
when we know each other well enough and our hiking styles (and their differences) well enough that we're very comfortable doing it, understanding what each others goals are,
and confident enough that we know we don't worry about the other if we don't meet up
if plans change. Alas, most of the people I would hike with are not like that, and I don't have
the confidence level in their skills (or them mine) to be able to sleep at all at night if they didn't meet up to camp. So while yes, the "partial partners" is possible, realistically, most
of the time, if you're with me we're connected because I'll feel responsible for your well
being.