Weight saving easy win
I've just put new 'bars and stems on both my kids' Specialized Hardrocks and frankly, I'm staggered - for the sake of 10-15 quids worth of discounted 25.4mm bars, and about the same cost on stems for each, I've saved a HUGE chunk of weight. I recall a similar saving off if my old P - Series All Mountain from a few years back when I changed the OE bars. We're talking hundred of grammes for tens of pounds.
Ok, the examples above are mountain bikes (and all Specialized), but if you've got a relatively basic off the peg roadbike, a decent weight saving on the ancillaries might be achieved for very little dough.