Adding this as I couldn't find any examples online and it took me a while to suss it out.

Taking a number value and creating a formula field to group into categories. In our case numbering the sites in a restaurant group.

If(${Accounts.No of Sites in Group}<1,'Not Known',If(${Accounts.No of Sites in Group}==1,'Single Site',If(${Accounts.No of Sites in Group}<=4,'Small Group (2-4)',If(${Accounts.No of Sites in Group}<=10,'Medium Group (5-10)',If(${Accounts.No of Sites in Group}<=20,'Small Chain (10-20)',If(${Accounts.No of Sites in Group}>=21,'Large Chain (21+)','Not Known'))))))