Microsoft
MicrosoftEd Hansberry Great to hear you now have access!
Old Excel would silently apply implicit intersection logic to its formulas to force single value results. Dynamic Array Excel no longer needs this as it can output arrays natively. So instead of implicitly intersecting, DA Excel calls out where this could have happened in old formulas using the SINGLE function. In your example, =TableName[Field] is a full column reference that only has one value but if you ever added a new row to that table, that very same reference would return multiple values and, in old Excel, it would have triggered implicit intersection. To ensure your formula continues to operate as originally authored, we show where implicit intersection would take place using SINGLE. You are free to remove the SINGLE from your formula if you do not want implicit intersection to apply.
TopN sounds like a great function candidate. Our initial focus is on getting Dynamic Arrays out with the 1st wave of functions but we are looking forward to unlocking more scenarios with future functions. If there is a function you'd like to see, please add it to uservoice so that we have a place to discuss the design and the community can vote.