How many areas is reasonable for areaServed schema?

I’m adding some schema to my site and was wondering about the areaServed property. Is this used for SEO in any way? If it is, is it good or bad to cram as much into it as possible?

i.e. if I simply added "Wolverhampton" (UK) as a city, would that be just the same as adding all the surrounding suburbs too? Would there be some benefit/harm in doing this?

"areaServed": [ "Wolverhampton"]  vs.  "areaServed": [ "Wolverhampton", "Wednesfield", "Bushbury", "Penn", "Bilston", "etc etc etc"]