Meaning of "if the shoe fits wear it" doesn't fit
Solution 1:
No, it doesn't have anything to do with the utility still left in an object or imperfect situation.
There is an idiom (or proverb) for a situation in which, when something is in a really bad/unacceptable condition but serviceable, then don't dispose of it.
The phrase is "make do" or, more frugal yet, "Use it up, wear it out, make it do, or do without."
If the shoe fits... originally it came from "if the cap fits...", which alluded to a fool's cap and dates from the early 1700s. It is thought that it changed to shoe as a result of the Cinderella tale.
"If the shoe fits, wear it" means, if something has all of the characteristics of a thing, it probably is that thing. More specifically, when a person has certain behaviors consistent with [unflattering label], then they should not object because they have been described that way. A person who acts a fool should not object to wearing a fool's cap.
E.g. Imagine person A is always prying into everyone's life, including that of person B. B doesn't like it, and says to A, "I don't like busybodies". A says, "Are you calling me a busybody?" Person B then replies, "If the shoe fits, wear it."
If it describes you, it probably is you.