Do you have to have a stir plate? Not really.
I'm a bit of a gear head. When I started all-grain brewing in 2009 I got any piece of gear that I thought I needed, which included three stir plates. I didn't really need three stir plates at the time because I was only running one 1 liter starter for 5 gallon batches. But it didn't take long until I upped my game to 10 gallon batches and two 1 liter starters.
My procedure was to pitch the yeast in the sanitized starter, put it on the stir plate, and wait until it finished out. This sometimes involved putting an aluminum pie pan under the flask to catch overflow from the too active starter.
At some point I started putting the starters on the stir plate for 6 hours until they became active, and then turning the stir plate off. At that point I would periodically swirl the flask manually until activity was subsiding, and then put it back on the stir plate until it was done.
These days I pitch the yeast in the starters, put them on the stir plate for one hour, and then swirl the flasks at about one hour intervals until activity subsides. I still put the starters on the stir plates when they are almost done, but I am no longer convinced that a stir plate is a necessary piece of equipment. Do they finish the starter faster? Yes. Are there any negatives to using a stir plate? Only if you object to cleaning up a mess on the bench where the starter krausened over.
I use mostly WLP-001, 007, 029 and Bell's House Yeast, and my experience has held true with these plus numerous others I have used over the years. If your experience is different I would like to know about it.
Note: I run 1L starters in 2L flasks, and 500 ml starters in 1L flasks. 2X volume is not enough to keep an active starter from kruasening over.