Here’s another case where brackets are clearer than commas. A sentence I saw recently said: We studied 693,111 tweets, by 13,102 users, that were geo-encoded in Croatia. That wording makes it unclear what geo-encoded modifies. Does it modify tweets or does it modify users?
The intended meaning is 693,111 tweets that were geo-encoded… Using brackets makes it clearer that geo-encoded modifies tweets:
We studied 693,111 tweets (by 13,102 users) that were geo-encoded in Croatia.
In that reworded sentence, it is clear what the relative clause—that were geo-encoded—modifies. It does not modify the material enclosed in brackets. It modifies the noun tweets before the brackets.
Here is my earlier post on brackets: In defence of brackets – Language Miscellany