Well, you can do that without ADB usb access, but what adb access will allow you to do is to issue adb commands from your PC to your Nook without having to use another helper app (e.g. Root Explorer (a pay app that can allow you to manipulate files on internal memory and remount the internal memory read-write) or Astro (free -- use to install apps that you moved to the SD card), Terminal Emulator (free -- use to issue command line actions), Wireless ADB (for those that can't get the drivers to install correctly on their PC), Email Installer (mail your apk to yourself as an attachment and install from email -- I love this one, myself.
I've tried to install using Email Installer and NC says
Installation of download apks is not supported
I think I'll have to do the ADB access for NC allowed me intall apks ...