I have 100% code coverage on a couple of projects. It has two benefits:
Behaviour is completely covered by tests, so changes in APIs which might break consumers of the library will at least be detected.
New work on the library tends to follow the 100% coverage by convention, so it's somewhat easier to maintain. Apps that have 90% coverage, for example, tend to slip and slide around. Having 100% coverage projects the standard "If your contribution doesn't have 100% coverage it won't be accepted". I don't think this is a bad default position.
Behaviour is completely covered by tests, so changes in APIs which might break consumers of the library will at least be detected.
New work on the library tends to follow the 100% coverage by convention, so it's somewhat easier to maintain. Apps that have 90% coverage, for example, tend to slip and slide around. Having 100% coverage projects the standard "If your contribution doesn't have 100% coverage it won't be accepted". I don't think this is a bad default position.