1/2-In main to 1 in supply line for sprinklers. Is this common?

[hometownhandyman]

Came across this the other day while I was working in somebody's crawl space. Noticed that the sprinkler supply line started as a half inch and was upsized to a 1 in. Is this common practice? I added a picture.

 

[Fitter30]

Probably didn't have a piece of 1". Could get away with it if a zone was under 8-10 gpm.