Any good military strategist should be able to utilise all resources by recognizing their stengths and weakness (this is always taught at military academies all over the world!!)
I have sucessfully utilised Militia not only for their 'battle' value but for their 'psychological' value. If you were playing against me as GER while I was playing the RUS, and I had 10 MIL lined up in at a shared boarder while still at peace, you would have no idea that was the case until you attacked me therefore you might line up more division than you should!! Once at war and you discovered an area with only MIL, I could play for time by using them to draw you into a trap then encirlce you!! Loaded with AA brigades as you sent planes to try and find more places where they were or were not, you would waste time and resoucres
The very fact that most players consider them useless is the very reason that I use them - they never suspect what I may be up to next ...