I have a z690 Classified. The only thing it really lacks on the z690 Dark as far as I use it (not XOC use) are the rotated socket and 2 memory slots instead of 4. I only use 2 slots anyway so I would have benefited potentially from only having two slots that can utilize a better circuit trace layout and thus host higher speed memory.
 
But I think your question is really why would you buy an EVGA z790 classified over some other brand's cheaper motherboard so let me shift over to that
 
If you're going to run stock settings (or even a very mild OC), you will probably be just as happy with a cheaper board, but there are some things that would draw me personally to the EVGA boards:
 
1. Warranty/support. I tend to base decisions on things like this to reviews and what I know about customer support. Most of the time when you buy a high end product, it just works and you hope to never need support, but there's always (and I do mean always) some percentage of parts that will have a problem, defect, or a maybe a compatibility issue or something and how that company handles those situations is important. I've bought many EVGA products over the years and while I've had a few problems and a few things I've not been super pleased with, they have overall been exemplary in customer support. I know when I buy something from them that if it fails or has workmanship issues, they'll take care of it. That's a huge deal for me. They also have, through the extended warranties especially, a longer warranty program than anybody else I've seen.
 
2. Performance. We've already covered that if you're running stock settings, the extra bells and whistles may not be apparent to you, but there's a benefit I'll point out. The VRMs are generally so well designed that they normally would need zero cooling whatsoever. They still put really good cooling on everything though...what that means to me is that I'm running the motherboard with the absolute minimum stress possible. I'm not running a VRM close to it's max temperature or current and then wondering why it died after 2 years. These were made for overclocking, which means they don't even break a sweat for normal use. So that sort of thing tends to lead to long-term stability. I'll add in here that the thicker the board, the stiffer it generally is. This can help with rigidity when mounting water blocks or even the massive GPUs these days as thinner boards will flex more and cause problems. It's a rare thing for it to be a problem with other boards, so this is a very minor thing, but it can be helpful. Added to this on the newer boards is the metal backplate. Pros and cons here as it is a little harder to maneuver and fit into some cases depending on the motherboard tray, but it can add even more rigidity to things. it also looks reeeeaaally nice, but the first time you pick up a motherboard this thick that also has a backplate, you will be surprised at how heavy it is lol.
 
3. Looks. I put it in a glass paneled case that I sit right next to while gaming and I really like the looks of it so that was part of the decision. I really like the darker more industrial or rugged look that EVGA boards have and I really like that they use more metal than plastic, unlike most brands out there.
 
So one thing I'll say against the Classified boards now...size! These are not ATX sized and you may run into some issues fitting them into some cases. Pay extra attention to things like right-angle connectors on the board and where those will point in your case. Some cases have grommets for the 24-pin cable way too close to where the board's right-angle connector is and you can end up with some odd cable runs to accommodate. The R/A connectors that point down at the bottom of the board are problems in cases like the Corsair 5000 series as their power supply shroud sits right below the board in some places. So just keep an eye out for that and plan accordingly.