Basically if your C++ function takes a pointer you need to write one for unique_ptr, or raw pointer (documenting the ownership).

With a GC, there is a global owner so you don't have to think about ownership for everything, this breaks down for some resource release (maybe half of objects) which is not necessarily easier. But typically GC languages also allow you to use RAII, though maybe not as consistently as C++.

What kind of programs can have unclear ownership? Basically everything that doesn't need to be high quality.