Europeans watch EU, North Americans watch NA, Brazilians watch Brazil. You go with whatever your time zone is and whatever you have time to watch, it has nothing to do with "casuals".
Indians watches the matches in India, KR, SEA and EMEA coz our time zone allows us to. NA matches happen from 12:30 a.m to 6:00 a.m so not a lot of people watch NA from here.