I really can’t say it any better than this:
Now let me make one thing absolutely plain. Dress codes are for the terminally stupid. Telling your guests what to wear implies that a) you are a megalomaniac or that b) you’ve invited such a bunch of witless fools, they’d all turn up in bearskin hats if left to their own devices. I simply will not go to any establishment that requires me to wear a suit, or a tie.
yes and no.
stating the dress code on an invite can give the party goer a hint as to the style of party planned. eg if it is a conservative or corporate cocktail party in the evening in the ball room of some fancy venue, then board shorts and thongs are clearly out of place. so saying blacktie or something similar on the invite makes this clear … although you could argue this could be explained or hinted at by other means …
whereas enforcing dress codes, that’s another story …