|Chew stogie, fire boltgun...|
The technique is one that I learned from a friend of mine back in my days as part of the Sheffield Irregulars - he was painting units up to sell on eBay, and all the units he did used this approach. One of the things we did at events was talk people through how to make these bases, which is also where I learned it.
The one downside with doing these bases is they do take a little time to make - and if you're doing an army like Imperial Guard, Tyranids or Orks it can be tricky to justify the effort across so many models. Part of the reason it has taken me over a year to paint up a 30-man unit of Conscripts was putting off doing the bases for the last ten.