What features are available when I connect my PC/Mac to the unit via a USB cable?

You can control DJ applications such as rekordbox (Performance mode).
You can input audio from your PC/Mac to the DJM-V10 or vice versa.
You can send MIDI signals from the DJM-V10 to software on your PC/Mac.

Before you connect to your PC/Mac via a USB cable, be sure to install the driver software.
For details, see [PC/Mac setup] in the Instruction Manual.
You can read the Instruction Manual [here].