Psychovisual Enhancements

[BluDChyLD]

I havent used this option before as in early DivX 5 versions it was causing problems. Reading a few posts it seems to be more popular now, a lot of people set it on strong. So is it safe to use now?
Thanks

P.S Does it increase compressibility or quality? I've read it stops the macroblocks in dark areas, is this true?