A similar issue as with the "-n" flag for netcat exists for "ls": Frequently "ls" is aliased by default in users home directories:

   $ type ls
   ls is aliased to `ls --color=auto'

On slow file systems (for instance, think of shared machines with large directories, NFS and heavy load) this can take ages to give output. Instead, if you just call /bin/ls, this call only calls http://man7.org/linux/man-pages/man3/readdir.3.html and thus gives output promptly.