Yes, just a basic check to tell you what volts it is putting out.
A couple of years ago, I had a problem where starting the car got gradually lazier and lazier.
I changed the battery, and after a week or so, the same thing was happening. I was measuring volts at the battery with the engine running, and getting just over 12v, so basically whatever the battery was managing.
I then changed the alternator for a reconditioned unit, and was disappointed to find I was still getting only 12v at the battery.
I then read about measuring the output at the alternator, and was getting 14.4v, as it should.
Thanks to guys on here, I then read about the earth points under the battery tray and also the one on the engine block.
I cleaned the earth points, the one on the block was quite dirty/corroded, put it all back together and was getting 14.4v at the battery with the engine running. It's been fine ever since, and the alternator was just a recon from the local motor factor, I don't even know what brand it is! It's lasted a couple of years already so I'm not complaining.
The point is, the earth points are critical to the proper operation of the starting and charging system, I suspect my original alternator wasn't even faulty.