If you are doing something equivalent to placement new on top of existing objects, the compiler often sees that. If that is your case you can avoid it in most cases. That is not what std::launder is for. It is for an exotic case.

std::launder is a tool for object instances that magically appear where other object instances previously existed but are not visible to the compiler. The typical case is some kind of DMA like direct I/O. The compiler can’t see this at compile time and therefore assumes it can’t happen. std::launder informs the compiler that some things it believes to be constant are no longer true and it needs to update its priors.

With placement new you need to hold on to the pointer. If you need to get an object back out of a buffer you need launder.

Std::vector needs launder.