In C and C++ we need to declare a function before its usage, if its definition comes after where it is called. (Well, there is also the "implicit declaration" rule in C, but it is rarely used.)
However, in more "modern" languages functions defined later in the same module are implicitly "declared" (or has the same effect as being declared). For instance, rust, python, etc.
What are other advantages and disadvantages of explicit declaration?