1. I omit the messages as ideally, they never get shown anyway.
It's much more important to add messages to preconditions, as they may get shown
2. I mean them often as comments. So commenting on them mean commenting better, but my point of laziness is pretty low. Writing
`assert 0 < x && x < modulus;`
as about as good as writing
// x is positive and less than modulus
It gives you already some information.
*You're formulating it as a reason against asserts, but what you want is more verbosity.*