Not only do they stop the user doing what they need to do but when they are implemented responsively, they are so often badly executed that they become usability errors in their own right. Sometimes as much as to lead to a critical error, and that’s unforgivable!
Pop-ups or light boxes only serve to distract users. Stakeholders like them because they hope that the user will stop and read an important thing that the organisation needs to communicate them. They are also sometimes used to ‘control’ the user’s journey which I also don’t like. So my advice is to please show, don’t tell.
OK, so you are trying to be transparent, which is commendable. But the question hasn’t been addressed about when is the right time to show relevant information and to do so clearly. Instead, be informative but don’t provide all of the information at once. It is still important to be clear but this kind of content could also be conditional and if it is important to mention then make it part of the page. Allow it to be expressed as part of the design.
Unfortunately many of our stakeholders use these as a way to express a thought rather than a solution. Instead we need to (respectfully) seek to understand what is important about what is to be achieved rather than implement something because we are being told to as a bad feature. This kind of content is usually part of the user journey; so make it part of the journey rather than as an exception which needs to served in a pop-up. Errgh!
Frazer Cooper 