Originally Posted by
LesterOfPuppets
I'd mainly consider how much replacement Cassettes and chains cost. If you get a new bike with fancy $150-300 cassettes and $80 chains then definitely keep the old one around.
If your new one takes $40 cassettes and $15 chains then it's up to you. That's not to expensive to replace.
Here in the Pacific North
wet, it doesn't snow very often where most people live. Instead, we get a rainy season. As Lester pointed out, the slop is pretty hard on drive trains - and also on rims (unless you have disc brakes). You wind up with a lot of sand and grit and all sorts of nastiness in the chain, grinding the cassette down, and when you use the brakes, it eats into the rims. So, a lot of us would rather wear down our old bike than the new, fancy one we (probably) just (or more recently) spent money on.
Plus it gives you an excuse to have a second bike. For a lot of people, it winds up being that your new beauty is your fair weather bike, and your older one gets rain duty.