It's just a way to tell you how many you'd need to cast on to make a certain pattern. So if a pattern has 4 + 1 it can be any multiple of 4 plus 1 more, so 9, 13, 17, etc.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry