It depends on how much you bet and where you want to support. In sports gambling of course you need to take a time where is ideal to make a bet like having research on the team, strategy, best plays and current lineup. When I make a bet too I do a single bet because at that time I can now watch the current live game and don't need to pressure too many indifferent bets. If you can handle in different game good but if you want to watch those games and get entertain go for a single bet at the end of the day still profit is the ideal thing.
The purpose of multi bets was either to net in as much profit as the user wants, or simply try to diversify the bet you want, just like how you diversify your portfolios. Though it still depends on the odds ofc, so it still requires a bit of judgment on that point. Honestly researching a team should automatically allow you to identify they're capabilities, letting you bet on multi-bets (or just deciding to go for single ones since you see no possible wins for multis).
I suppose this is a central point in this discussion here: In a multibet you can bet with smaller amounts of money and still get huge gains. The fee might be higher but you also leverage your money in a sense. So for the occasional bet with small money a multibet is very attractive. It is a different story if you want to place large bets, then fees become more important and often large bets are for a single event only
Multi bets simply give you more opportunities to net money from bets (and also lose more).