The big advantage of a monorepo is that dependency on changes to a "library" or component that gets reused in multiple places can be made explicit. A user can c

The big advantage of a monorepo is that dependency on changes to a "library" or component that gets reused in multiple places can be made explicit. A user can commit a change that safely modifies a library or component in a non-backward-compatible fashion AND changes all the places that use it. This is far simpler than the alternative of releasing a non-compatible version of the library/component and maintaining both in parallel for a period while the users transition. The big advantage of separate repositories is that the work done on them is very clearly marked as independent. It becomes easier to take one component out and utilize it elsewhere... but at the cost of having to deal with dependency management. Dependency management is simple and automatic in easy cases and really terrible in hard cases (like when two components you use mandate mutually exclusive versions of a third component). So I think the driving factor in the decision is the tradeoff between the degree to which you are willing to invest in careful packaging of each component (and the corresponding dependency management), versus your willingness to force everyone and everything to utilize the monorepo. (Notice I didn't mention performance issues. I really don't think they are important enough the control the decision.)