We often have a 2nd person help at the start and end of the cut by holding the end of our mill like that but always wearing safety gear. Once the cut is started we usually get a better finish with just one person operating the mill as one person can control it better. Sometimes you need a bit of assistance when going through a side branch or other feature. With a good sharp chain and the log sloped sufficiently it's better to work on your own.
We're also about to get a slightly shorter bar, which is obviously much safer on narrower logs. Also more powerful as the chain is shorter.
If you're thinking of a new saw for planking - we manage ok with a Stihl 660 with 30" bar. If you're getting it specifically for planking you can get one with a different oiler which allows more flow to the bar.