I do a lot front end development with Magento, and one of the biggest time sinks for this is waiting for a page to load when you want to change a line of CSS.
Whilst you can use Firebug / Chrome to edit CSS rules on the page, you still need check that the file is saved correctly. As this is Magento, this can take some time due to caching being disabled.
Thankfully there is an extension for Chrome which will just reload you CSS files and not the entire page. You can install it here and save a lot of time during development!