** EDIT **
Absolutely - If you're pitching a design for a NEW client/site. Lay-folk generally have a hard time seeing what's in your(my) head. Wireframes, drawings, etc. don't always cut it either - scratch that - they don't cut it. I hear more, "I thought it was going to do X" from clients when all they have is a WF, or sketch than I do when they're given a mockup with their logo, photos, corporate fonts, and a UI.
Any other scenario:
Maybe not - If can use existing HTML/CSS/JS that matches the job requirements, or you're editing content of an existing client, you'll be better off working just in the code. If not, you're probably going to waste a gross amount of time in Photoshop for very little return. There are those instances (like @DAO1 mentioned) where a screenshot and tweak-via-Photoshop can really speed up an approval process, or hammering out an idea, or three.
** end **
I say yes -
It's a lot easier to sell your designs (and much quicker to create comps) with a visual - even if it's simplified. That's where PS is most helpful for my jobs.
I also incorporate a layer with a grid system, so I can see how things are laid out, and quickly drag them to where I need them. Again, this helps with comps, and client-requested changes.
If you keep a Photoshop library of your commonly used elements: vector based rounded corner input boxes, your grid(s), "logo goes here" box... all in layers of a single file, or multiple files (your choice) - you'll be able to build home pages and interior pages in a fraction of the time it takes to code them.
Keeping a common CSS file (with popular settings) will also help when it comes time to code, but I don't see the value of eliminating PS from the work flow - regardless of how robust CSS becomes.