I don't think MC places any specific meaning on the Grouping field and things won't be automatically organised based on what's in there, it is just provided as a convenient tag for you to populate as you wish.
If you want to be able to filter and sort by the Grouping field, or any other field for that matter, then I think you can add the field to the list of columns that is displayed and filtered by (there's probably an wrrow or some other symbol on the column heading line), or you can create a custom (category?) view which includes Grouping in the level between Artist (or Composer?) and Album?
I use Grouping to deal with boxed sets, i.e. multi-volume CDs. The overall boxed set name goes in Album and the individual CD titles go in Grouping, and Disk # is also populated as necessary. Anywhere there is a view with a category of Album, I have instered a level before it which is an expression that evaluates to Grouping if it's not empty or else Album.