OBP,
You're exactly right with part time 4WD. You can disengage the front driveshaft, and if it’s equipped with lock outs on the hubs, you can disengage the front axles and differential too. It's a much more versatile system with less wear and tear on transfer case, u joints, and front differential, and gas mileage is usually better as a result. However, the Blazer we're referring to here is a 2000 and it's equipped with full time 4WD. I'm not certain, but I believe GM went to that system with the second generation T series. Most of us 4X4 veterans know the difference, but someone reading this may not know the differences in the two systems.
OM