I find 1) to be a good property assuming you have some safeguards or rollback procedure, at a cultural/code ownership level it moves the efforts of shared-code changes on the person doing them rather than on the ones depending on shared code, which reduces communications, frustration points and increase responsibility.

For instance in multi-repo environments I've often seen this pattern: own some code, bump an internal dependency to a new version, see it break, ask the person maintaining it what's us, realize this case wasn't taken into account, few back and forth before finding an agreement.

On the other hand in mono-repo environments, it's usually more difficult to introduce a wide changes as you face all consequences immediately, but difficulty is mainly a technical/engineering difficulty rather than a social one, and the outcome is better than the series of compromises made left and right after a big multi-repo change.