In the US, it's very common to add a comma for numbers of more than 3 digits (ex: 1,000 for one thousand ; 1,000,000 for one million ; etc.). In France though, we don't use this at all and commas are ...
This may sound like a stupid question but I'm being taken to task for this at the moment. Personally I believe that it's easier to read 1,234.56 than 1234.56. However there are others that are saying ...