Your sims get different moodlets from drinking nectar (see the list on
this page). Some last up to 8 hrs. If the nectar was made with flame fruit they'll get the warm/cozy moodlet. If the nectar was made with enough life fruit your sim will get a day younger. I think nectar made with plasma fruit will satisfy a vampire's thirst, but I've never used it for that. Beyond moodlets though, nectar doesn't confer any special benefit like herbs do. In that way it's just like most other skill based means of making money.
As far as I know, the Bohemian Garden fruit is equivalent to using apples in nectar making as far as recipe value and taste (i.e. amazing vs. terrible).
I don't guess with nectar recipes. I use
this list a lot, or
this list. I use
this mod as well; I haven't discovered anything better than what I've found online with it though. I find the mod useful when I have a bunch of random fruits to use up and I let it pick a likely good combination.
I mainly use nectar making for money. I age the nectar as long as I can stand and then consign it. One household made 1.4 million from their nectar hoard. I'd have sims drink it regularly for the moodlets, but you can't hire maids if you do (they'll throw away glasses of served nectar) and I usually forget to have my sims drink it regularly. :p But that would definitely be a strategy to keep your sims' mood meter maxed.