One is definitely not enough! Or, more accurately, one Home Thought and another three or four "bookmarks" with accelerator keys similar to Set as Home Thought, plus the same number of accelerators to recall these saved Thoughts (maybe the PgUp, PgDn and End keys when the plex has focus).
The Pinned Thoughts bar is useful but can readily overflow when just one thought with a long name is pinned there. I find setting and recalling the Home Thought much faster by just using the keyboard; there is no need to reach for the mouse each time to unpin and drag a thought.
I employ the Home Thought not just to locate the top of the thought tree but also as a handy though much overused bookmark. The problem with doing this is that occasionally when I try deleting a bunch of thoughts, one is not deleted, and when I try deleting it I get told I can't, because somewhere along the line I already set it as the Home thought and the Home thought can't be deleted. Rats. Another good reason for having extra bookmarks that aren't subject to this rule.
Apologies to anyone who has requested this before, though the search engine turned up nothing.
On the subject of the Home Thought, SpaceNexus (Jim) made these suggestions:
Can we add a parameter to Tags to be able to 'Set as Home Thought', in addition to the existing Pin.
How about a toggle option in preferences to start with Home thought / last thought when PB opens?
I don't know whether either of them has been implemented in v6 yet, but I endorse both of them.