See this is one of the few things I agree with the Americans on. When punctuating a sentence, you put a comma in the places where you pause but not stop, to help with legibility - and then a period at the end, to differentiate from the next sentence. When writing a number, I like to put commas in the number to help with legibility (1,000,000), and then a period at the end to differentiate from the decimal part of the number (1,000,000.000).