Then there's std::string. Super nice in 95% of cases but can cripple an application if you have millions of strings you need to deal with (TONS of dynamic memory allocation).
And then there's std::shared_ptr. Super convenient but potentially a huge impact if you have items with very short durations in hot loops. std::unique_ptr on the other hand has no added overhead. Sure, you can look these things up. But it's not really obvious.
C++ is an incredibly useful language. It's far from the safest, prettiest, etc. But when used properly it's a very powerful tool. But knowing C can help you to better understand when you're not getting something for free and when undefined behavior can rear its ugly head.
Being aware of what is happening and the best tools for the job I suppose! And knowing the STL inside out and its idiosyncrasies and foibles.