The vast euphorbia family includes both saints and sinners, plus a few marginal members on whom the jury is still out. They're ALL poisonous, but in some cases this quality is actually venerated. Our pharmacopeia is full of toxic substances, and knowing how much to use makes all the difference, as the physician Euphorbus advised King Juba II so long ago.
For me the marginal class of euphorbiae is exemplified by gopher purge I gladly tolerate a certain number of volunteers each year and will let one or two grow tall to reseed. Why? I like their looks at all stages of development, and they're easy to pull out. I like knowing that they're used for "mole and vole control" as well as their eponymous function.
I am leery of the candelabra tree. Its nocturnal blossoms are lovely though short-lived, but Russell's grew about 20 feet tall and, swollen with rainwater, crushed his aluminum garden shed when it fell. That must have been in an year. 1983? 2010 may be a good year for some drastic pruning.
Poinsettia, of course, is one of the saints. I am tending a tiny one that was a Christmas decoration for my parents this year. With any luck, it will grow up to overcome the influences that made it bloom ahead of its natural season.
Petty spurge is an out-and-out scourge. In my book, it has no redeeming qualities. Each tiny annual plant makes hundreds of seeds that can wait many years for the ideal sprouting conditions. Alas, that time is NOW. Our parking strip is crawling with them.
Petty spurge both causes and cures skin diseases. This ambiguity makes it attractive to cancer researchers, but I doubt they will come and take my noxious weeds away. Meanwhile I will spend many hours on the sidewalk and curb making room for violets and allysums.