Our players played LMoP for a 7 hour session. From this, they learned that surprise is huge. So with our new campaign, we have 2 PCs with 16 Dex, 3 with 14 Dex, and 1 with 12 Dex. Also, 3 or 4 of the PCs took stealth.
With these new PCs, we just played our first 8 hour session of HotDQ yesterday.
Since surprise is so powerful, the players reacted by creating PCs that could take advantage of it. We went through HotDQ and since it was nighttime, almost all of the encounters the PCs had surprise (2 encounters, they only had surprise over some of the NPCs, 5 encounters, we had full surprise). In that same timeframe, 1 PC went unconscious twice, another got seriously damaged twice, and a third got about half damaged. The other three PCs took little or no damage. In 7 encounters. Granted, the PC fighter is fairly heavily optimized with Heavy Weapon Master, but even so, the DM told me that these were 2 easy 3 medium, and 2 hard. I was running a Wizard who never once cast a first level spell (other than Mage Armor) and never did more than 4 points of damage (at least 8 of them were a 1 damage on the roll, the players were laughing so hard every time I rolled a 1, yet again). Even with my PC being mostly ineffective, surprise made these encounters a bit of a joke. Even when we were outnumbered (2 encounters outnumbered, 2 the same number, 3 fewer foes), it hardly mattered.
Anecdotal, sure. But, the same applies to Advantage. If you allow the players to use it frequently, then encounters start becoming a lot easier.
My take is to use advantage when the rules state to do so, otherwise, do not.
If the DM wants to give a player a bonus, it should be +2, not advantage. The same with disadvantage. Give -2, not disadvantage. JMO.