My experience with IWYU has been mixed. In general it's a success. But it had trouble identifying that some headers were only conditionally needed (eg, debug build or macro conditional). Those cases are easy to work with if you own the code but can be annoying if it's in a third party lib.
That said, I do highly recommend its use.
I've found that using IWYU Pragmas [1] for codebases you own and IWYU Mappings [2] for third-party libraries __almost__ entirely eliminates weird IWYU suggestions (there are a few annoyingly stupid suggestions from the tool I just ignore).
I've also recently been making libraries I write compatible with users that run IWYU by annotating all public headers with IWYU pragma comments that export symbols/transitive includes correctly, etc.
[1]: https://github.com/include-what-you-use/include-what-you-use...
[2]: https://github.com/include-what-you-use/include-what-you-use...