What is the difference at runtime between !a and a == nullptr in the real world?

When I am checking whether a pointer is nullptr in my code, I would like to use if (a == nullptr) since it make more sense to me. However, I see most senior programmers and tutorial codes like to use if(!a) instead. I know what it means, but this way is just not as straight-forward as the former one for me. I just wonder, will these two ways of if checking cause big a runtime difference in real world projects, like when we need to use this if statement thousands of times?