For those with the RAM to spare, this seems like sensible behaviour -- If there are ways to speed up your web browsing by using otherwise idle RAM, then great!

For those with the RAM to spare, this seems like sensible behaviour -- If there are ways to speed up your web browsing by using otherwise idle RAM, then great! Unfortunately, the flipside is that if you're using a computer more than a few years old, then anything more than your set of 'core' sites tends to slow your computer to a halt as your browser causes everything to be constantly swapping in and out of memory.