You don’t have to bet on all the games, mate. You need to only bet on the games that you think have less risk and more chances of winning. At the end of the day, you are betting through your hard-earned money. Hence, you need to be very careful while choosing the games to bet on. It’s always beneficial to bet on the games where your favorite team is playing, as then you will know the strengths and weaknesses of your favorite team and bet accordingly. People do betting in order to earn some “extra” cash. So there is no need to bet on each and every game.
Sorting out those few games that you will be familiar with has to do with time. The person needs to have time to either be watching those games and make his or her conclusion based on the game result or they need to check through available data online in order for them to know each team's strengths and weaknesses.
If a favourite team is playing, sometimes there can be some biassed judgement that could be made toward such a game. Based on the love and support you develop for one particle team, how you will predict the game on them might be affected, as there are greater chances that you will end up always trying to bet on them in situations where they will have to win.
Unless your strategy of playing is the reason why you made them your favourite, if not, if it's a team you support, I prefer to avoid placing bets on such games.