Looking straight up is hard.
Physiologically we're supposed to look forward, right? Presumably for predators out in the tall grass of the savannah. Not a ton of trees in the savannah, so why would we need that kind of neck mobility? Then there's another couple 100,000 years of farming and hunting ultimately culminating in watching Gilligan's Island. So looking straight up? Bah!
But then we go underwater. And all the sudden looking straight up is way, way better.
Because in an appropriate dive position, "straight up" is forward.
We spend a lot of time, particularly in cave diving, stressing the importance of proper trim. The moment you drop your knees your fin-wash hits the bottom every time you kick and anyone swimming behind you will spend the whole dive struggling with bad viz and cursing your name.
But that's not the only benefit to 0° trim. Which is why it surprises me that in open water people tend to tilt into varying degrees of far less efficient body position. People argue that there's plenty of room... so why bother holding an uncomfortable position?
Think about seals. About dolphins. Torpedos. DPVs.
Let's say you're riding a DPV, but you've got to keep it pointed at about a 45° angle the whole time. Are you getting the most out of it? Are you going to be able to get full speed and/or torque?
No. You're going to burn out the battery in no time because to try and make any headway holding the thing in that position is going to chew up so very much energy that you might as well have just left the thing on the boat.
Dolphins don't swim at a 45° angle for the same reason. Flat and hydrodynamic is efficient. Being able to kick and then glide for a while, expending no effort at all, even having a mini-vacation from workload between every kick, is economical.
Or, let's say you're in current or flow. Do you want to be in a position that lets the water flow generally around you without having to fight? Or do you want to look like a giant goddamn sea-anchor, huffing and puffing and fighting like blazes to even maintain your location?
Why bother holding an uncomfortable position?
Because if you do it for long enough it becomes very comfortable. It becomes second nature... possibly even first nature. (I don't tend to swim a ton without dive gear on, partially because as soon as I feel wet I have to fight the urge to go into foot-up flat trim.) Look straight up for long enough and the flexibility in our necks will accommodate the oddity perfectly comfortably.
And here's the key point: When you develop that muscle memory, your body just holds position automatically. So that if you are caught in a current, or cave diving, or suddenly a problem erupts that you need to focus your attention on... your now-focused attention isn't required to hold the best possible position to move as quickly, calmly, comfortably, and burning the least calories. Instead of suddenly floating into perfectly vertical trim and now fighting to even stay at the same depth (when vertical your movement up and down through the water as you breath will be GREATLY exaggerated).
Oh also: wanna see your SAC rate plummet to nearly-nothing? Be properly buoyant and trimmed, moving through the water like a human torpedo.
Or... I dunno... maybe you consider diving your exercise regimen and really, and truly enjoy working way too hard to move around?
So, yeah. Even when you're in open water, try not get sloppy with your trim. If you're having a tough time getting to where you can simply float, without movement, in a perfectly flat -- there are a ton of great instructors out there who can help you stick that landing. Reach out to one of them. You'll be absolutely amazed at how big a difference in makes.
Yeah, looking straight up is hard. But it gets easier and easier. And it is very well worth it.