Agreed with Dan. As a contractor we got good enough at just connecting two dots. But a chalk line insures a straighter line. We did left side. Before airless we had pointers so this was more important. With airless machines the gun acts as to pointer.
Speaking of pointer… Here’s two.
Many stripers use asphalt shingles at start of each line. It insures more consistent and straighter starts.
Lastly we use to sell a Pre-mark real. It was a measuring tape premarked with measurements for different striping scenarios. They were great especially for beginners. We just did not sell enough to keep in stock. I am sure you can still get them.
Have a great day!