In fact, /lib64/ld-linux-x86-64.so.2 is set as the interpreter of the dynamic executables, so executing ./dyn_exec ends up being equivalent to /lib64/ld-linux-x86-64.so.2 ./dyn_exec. The explicit form is sometimes useful, for instace if you want to execute the file with an interpreter other than the one specified in the executable, or if you want to pass one of the parameters that ld.so accepts.