as has been discussed here before, one of the main things you're likely to notice is reduced rotational/angular intertia— ie a lighter rim, tube, and tire. this makes your acceleration 'snappier' as you're not fighting as much weight into motion.

this is one of the main reasons (but not the only one) that open pros, at around 435g, are often recommended over deep Vs, at around 580g. however, if you're going to throw on a thick, wire-beaded tire, you may as well save your cash. quality tires will weigh less and have better road feel, but often won't last as long.