A brewmaster friend of mine runs a highly respected production micro brewery. I have had the good fortune to brew on his production 10 barrel system a number of times. Water is added first to a point, then grain is added one sack at a time and stirred in as aggressively as possible without splashing as water continues to flow into the mash tun through a sprinkler ball.
For him, at production scale, he is concerned about both keeping the consistency of the mash thin enough to work with (it's like stirring wet concrete with a giant paddle, extremely difficult) and keeping the pH/temp of the mash within his desired range throughout the mash-in process.
Although being extremely concerned with those variables may be less important to you in your home brewery, I use his technique to the best of my ability with my 10 gallon system and I am certainly pleased with the results.
I agree with the previous posts. I'm just overly particular and love to learn whatever I can from the pros!