In my mind, it is always a win to go to a C++ conference.
There are still managers who are against sending developers to conferences, for their own reasons, many of which I disagree with.
Not because I myself am a C++ developer, but because, as a community of developers, we do seek the opportunity to grow, to learn, and to connect with other developers.
Having the opportunity to do such things keeps developers happy, and being happy, means developers have more drive to deliver.
If you need a listing of reasons why to send your developers to a C++ conference, then have a look at http://slashslash.info/2019/05/reasons-to-send-your-developers-to-cppcon-or-any-c-conference/