ive made 2 starters ever homebrewing
making a starter is important if you are introducing your yeast into a quite hazardous environment
I.E large amounts of fermentable sugars, odd temperatures, pitching along side bacteria/another yeast
or if you are propagating from lets say a single cell to a pitchable amount, or like going from 5 gallons worth if pitchable yeast to a 1bbl batch and you want to have proper pitching rates
stir plates allow for proper oxygenation of your starter, and usually a better viability count
example, at Southern Tier, we would make 6 2000ml starters, and dump them into a 15bbl turn, then let it prop up, do another 7bbls into the propagator, wait another 6 hours, and pitch another 7 bbls into it for a total of a 30 bbl starter. Wait a day, and then pitch the entire thing into a 220bbl batch of IPA, Pale Ale, or Uniwheat, which we used for the blueberry/raspberry/and Chautauqua Brew.