[bombcar]

Price is a good stand-in for it, and it helps encourage "landfill rescue" - buying a shirt at goodwill that would otherwise go into the grinder is better than almost any other option for acquiring a shirt, even if it's a relatively crappy shirt.

Part of the issue with it is that what is "most energy efficient/best for the planet" for a single user may not scale up to what is best for everyone to do.

There's also a problem in that future years of function cannot be estimated well or reliably; the average American kitchen will last 40-60 years, but be remodeled in 10-15 years. Since you cannot control what happens after your house is sold, you are better off using another calculation (or assuming that the purchaser of your house will bulldoze it or something).