Not many of us are playing using an account that can battle competitively for a leaderboard spot. If you are on one of those, by all means don't surrender. If you are not, though, why even bother trying to battle against level 7 and level 8 summoners? The power gap from gold to diamond is almost as huge as it is from silver to gold. Just give them the win.

Time is money, and so is your Energy Capture Rate. If you are multi-accounting, surrendering will leave you more spare time to play on different accounts. If you are on a single account, you get to not be as frustrated for going on a 20 matches long goddamn losing streak because every single opponent is at 3700 or 3800 rating, absolutely decimating you no matter how well you use your cards simply because they own more stuff. Surrendering games you know you can't win lets you get that daily done in less than freaking 30 minutes.

Here's a guide to quickly understand if your account can win! Look at your opponents' last played matches. If the same splinters on their history are available, look up their summoner and monsters. Sometimes they might hold a level 8 summoner, but the monsters don't add up. However, if you see they are using a bunch of maxed legendaries, you can just skip even trying unless you got the Rise of the Commons rule, where skills matter more than usual.

Another hint is watching for the mana cap if you're only using older cards which usually max out at 6 mana. Even if they are not using maxed monsters, as long as they own higher mana cost monsters than you do, you're screwed. Some of my teams on average can't get past 30 mana, so it's a waste of time trying to win those 45+ mana matches. In case you haven't figure this out already, you should invest in some high mana cards once you reach Diamond, because the mana cap is consistently increased.