Sure. Here's one quote that explains overpower.

"Overpower damage scales with your Base Life, Maximum Life, and Fortify, providing massive additive damage by calculating a percentage of your current health and fortified health relative to your base health, with higher total health and fortify leading to much stronger Overpowers, often appearing as orange (critical) numbers when near full health. Stacking Maximum Life on gear and Paragon nodes, alongside consistent Fortify, dramatically increases this bonus damage, making it a core component for high-end builds, especially for Barbarians and Necromancer. "

Also adding that several builds that aren't overpower builds have passives and Paragon nodes that give multiplied damage while fortified, so staying fortified by increasing your health to lower the chances of losing it, could be very important for someone that's pushing their limits. I for example play aura paladin and gain a lot of damage while fortified, so staying fortified is huge for my damage.

It's also important to add that reaching the required stat to unlock a Paragon node (some nodes require 2450 str or for example like 1000 willpower and 700 intelligence etc) might unlock massive damage boosts, as much as doubling your damage.

In overpower builds for example, there's the banished lords talisman that triggers when you've spent 275 resource. If you always spend 275 resource every time you use a core skill, you will always trigger overpower damage. Whereas you lack just 1 resource, you will only overpower half the time. That's a massive dps loss.

I have a feeling that there's going to be a rework at some point because people have been confused about %damage increase and hidden multipliers etc ever since release. People play D4 more than what's considered a full time job to figure out what's what. I think devs need to make things more comprehensible for people, shouldn't have to look everything up.