Resolving conflicts between third party typings from DefinitelyTyped has cost me a lot of time over the last couple of years. The typings we use are maturing a bit, but at one point someone merged a completely unnecessary refactoring of the React types that caused compatibility problems for months until all other dependencies were upgraded.

Using yarn.lock means it never breaks unless we specifically choose to upgrade though, so it's still worth the increased productivity and safeness from TypeScript, which is awesome as a language especially combined with VS Code.