When should web designers use modal overlays?

[piratejenny]

@anon36081309

The ones I find most irritating are the ones that prompt me to sign up for the email newsletter the first time I visit the site, before I even see the content I came to see.

YES. I have a vast menagerie of pet peeves, but this is a big one. “I just got here, I don’t know if I even like you yet . . . but now I automatically like you less.”