If your goal is to keep a local copy of the repository for easy backup or for sticking onto an external drive or sharing via cloud storage (Dropbox, etc) you may want to use a bare repository. This allows you to create a copy of the repository without a working directory, optimized for sharing.
For example:
$ git init --bare ~/repos/myproject.git
$ cd /path/to/existing/repo
$ git remote add origin ~/repos/myproject.git
$ git push origin master
Similarly you can clone as if this were a remote repo:
$ git clone ~/repos/myproject.git