It allows to quickly and effectively communicate with the desktop computer. Using HID means that this oscilloscope does not require drivers (only the oscilloscope software).
http://www.semifluid.com/PIC18F2550_usb_hid_oscilloscope.html
This is a simple PC voltage oscilloscope using only a PIC12F675, a 20MHz oscillator, and a RS232 level shifter.
http://www.semifluid.com/PIC12F675_Oscilloscope.html
sweeps out seven logarithmic-scaled currents from 1 ľA to 1 mA while measuring the voltage, 0 to 5V (3.3V on some PCs), at each step
http://www.edn.com/article/CA170223.html
http://www.edn.com/article/CA158985.html
produces an oscilloscope trigger that synchronizes the horizontal sweep to a video signal that allows you to view any horizontal line by adjusting a potentiometer
http://www.edn.com/archives/1996/090296/18di2.htm
A very nice article on the actual use of O'Scopes.
http://www.tek.com/Measurement/App_Notes/XYZs/index.html
How to test those pesky transistors with a DMM or VOM.
http://www.anatekcorp.com/qdmmvom.htm
The proper techniques for using an oscilloscope are presented. From basic measurements to more advanced techniques.
http://www.doctronics.co.uk/scope.htm