parts
Pardon my parts ignorance...but: my bike (well, I have two others, but this is the only one I really ride), an Independent Fabrication, si 14 years old. Recently was having lots of shifting problems, including a really strange one: a number of times, the chain came off of the cassette, and got wedged between the wheel and the cassette. A number of trips to LBS (a high quality, very reliable place) didn't fix it, and finally, they decided to replace much of the drive train. Chain and cassette (those, of course, have been replaced many times), one of the chain rings (I have a triple) and the rear derailleur (the front was replaced 2 years ago).
Not it's working much better, but do to availability these days, these are lower grade parts than Ii've usually had, like a 105 cassette instead of ultegra, tiarga chain instead of ultergra, deore instead,...
How much difference do these things make? I really don't' know.
If it's just wieght, for my life, style and purposes, it doesn't much matter.