I'd would like to know all the reasons to avoid popups in a website (in a web design best practices point of view).

Ex : doesn't use all screen space, needs Javascript...

+6  A: 

It annoys people and that's bad for your business.

Jouke van der Maas
Yeh, "Everyone will hate you" seems like a good enough reason to me :)
+3  A: 

The question should be What is a remotely good reason to have popups on a website?

There is no answer to that question.
Jouke van der Maas
@Jouke Yes, the answer is "None"
Bart van Heukelom
@Bart You are truly a genius. Or I'm a moron. Or both.
Jouke van der Maas
@Jouke The answer there is "Neither" :p
Bart van Heukelom
+1  A: 

To me, it depends on what kind of popups.

If you're talking about the old fashioned, new window, ad-filled annoyance popups - avoid them at all costs. They are damn irritating. Everything that only/99% of the time annoys the user should go away, simple as that.

However, if you're talking about popups as in modal dialogs or small information windows in an application, those are usually fine. It all depends.

Arve Systad
Modal dialogs has the benefit of not forcing people off the current page.
Gert G
+2  A: 

Accessibility. It confuses people with screen readers.

Gert G
+1 I didn't even think of that, very good point.
Jouke van der Maas
+2  A: 

Every browser has a pop-up blocker these days, so your users will be forced to allow exceptions for your site. Personally I don't tend to go back to sites with popups.

As many organisations don't allow their employees to change settings like this, you could potentially be stopping your site from working for a lot of people.

Damien Dennehy
+6  A: 
  • Most browsers disable them automatically
  • They do nothing positive for your Search Engine Optimisation
  • They break the natural flow of a website
  • A user will instinctively consider the website untrustworthy/spammy
This is probably the best answer to this question, but it has the least votes. I did what I could.
Jouke van der Maas
Thanks Jouke, the force is strong with you :)

Many sites are using pop-unders, but I find these annoying too. I have seen recently people are using slide-in strips at the top or bottom of the page.