Oh yeah, the bit where SSDs move sectors around for wear evening is important. Because of that, it's possible to completely fill up an SSD after deleting files and still have those files recoverable from the flash chips themselves. Without that secure erase, as I understand it, if a sector gets marked "bad", whatever data is there might stay there forever (or at least as long as the cells hold a charge).

So there's no benefit to writing multiple passes over deleted data on SSDs as far as the flash is concerned, but multiple passes might make it more likely for the controler to actually direct those extra writes to a sector actually storing the data (though the odds might be low unless you're overwriting all free space, though even that depends on how much space is free vs how many "spare" sectors there are, and even then it might be impossible to get it to write to a sector marked "bad").