80% of client side optimization can be done in 2 hours or less. Research shows time and time again that faster websites convert and retain vistors better. It's worth the 2 hours no matter what stage your project is.
I have to disagree with you there. Some optimization steps significantly hamper development and should be saved until near the end of the project. For example, JS minification is very fast and easy, but it makes debugging much more difficult.
And you shouldn't compile things into CSS sprites until you are fairly settled on what images you'll be using. If the look and feel of your site is still in flux, you're wasting time by making sprites.
Use automated tools to minify files on production but not on your development server or localhost.
I'd put CSS sprites into the 20% you do later. Some images are very simple to merge and don't change (such as icons) but the rest, yeah, wait until you sort it out.
>Use automated tools to minify files on production but not on your development server or localhost.
Yeah you can do that, but there are still points in the project where it makes little difference to do that, and it's not hard to get stuck in those points.
Of course, once there's wide support for source maps, you'll be able use minification even in development.
Considering how much most pages can be optimized, its a good tradeoff. How often do you refresh during development? How much time are you waiting for that reendering?
