Butter is awesome, I had a butter only snack (100g) out of necessity years before I could even imagine to try carnivore - but it was still enjoyable. I always loved fat too much (sadly, I need to eat way less than what I desire just to maintain my fat body… though I doubt I could gain even more but I hate overeating massively… but I digress) and butter is very tasty fat!
I don’t eat much butter for reasons (the fat minimization I have been doing since I went low-carb… I pretty much avoid added fat, as much as I can, at least but I am good enough at that now, after 1.5 decades) but it’s a joy every time. My fat fast days always have a cute portion
I don’t really need any added fat to reach 90% fat, pork is enough - but butter is lovely. I rather skip egg yolk than butter on fat fast days…
It’s an expensive item and anyway, I love lard too but one just can’t replace the other. So I keep both and if I had to choose, that would be butter. I have plenty pork fat in my meats, I don’t need so much rendered out lard… But it’s good to have both.
I don’t cook with butter or put it on meat or anything, only use it in baking sometimes (but not on carnivore, there I like to put it on my baked goods).
I used to use butter almost exclusively on bread in my past. The pure butter eating came later but I do it sparingly and the amount isn’t so big. But it’s very, very, very nice. I disliked it in coffee though, I need some more proper dairy there.
Eating a big slice alone again… It would be a LOVELY way to add fat if I ever needed it. But as I wrote, I don’t. Not even on fat fast days. But maybe I will do it one day. I just love pork jowl too and I only can afford it on fat fast days or else I will massively overeat, almost no matter what. It’s a bit hard to stop. Butter is great but I can stop easily. I know as I often eat a slice when I put another portion into the butter dish… Or maybe use it for something… It’s quite irresistible, that’s why it’s good to be able to stop early.
Well I eat way too much fat, fat doesn’t help with satiety unless it has a ton of protein too (but my protein sources usually have enough. they had way too much until I trained myself to eat lean pork) - except fat fast days… But yes, it’s a good snack. Sometimes. I mean, I want to chew on things too. Like the hobbits with the ent drink, nice, good, satiating… But a hobbit want to bite into their food too! 
Wow. When I was a kid, I merely ate mustard that way! (Still love sour things.) I put the butter on half a loaf of bread… Your kid does it better! 