I like sloped tips but they are not a must for me provided the tips are not to chunky. I'll shoot straight or sloped but I probably prefer sloped. Anything between a 10 to 15 degree slope angle works for me.
I think there are two, maybe three advantages with sloped tips? The first one is the perceived advantage of having less contact area with the bands. I think it feels smoother and lighter to draw because of the reduced friction. I don't have any experimental comparison to back this up so it's just an impression. It might also enhance bandset longevity but I don't know for sure? For me, the smoother, lighter feeling draw is its main appeal. I will add that the contact edge should be gently rounded over so it won't cut but not too much or it might throw off shots.
The second possible advantage is shooter specific. Sloped tips allow for forward canted or straighter wrist shooting. So if you tend to forward cant a little then sloped tips will be more forgiving. However, If you don't forward cant and hold your frame square, the sloped tips won't make much difference other than reducing band contact. You can shoot sloped tips holding the frame square. It makes no difference imho. I will also add that whether you forward cant a frame depends on the rest of the frame design also - how the swells are implemented and the shaping at the pinch area will influence how a frame sits into the hand.
Thirdly, though this is not really just about sloped tips, is that a thinner fork tip profile is preferable by most shooters (I think). We just don't like seeing chunky tips, probably because they just feel clumsy? Thinner tips seem much cleaner and feel more agile and I think this influences accuracy by not contributing to the mental detraction of clumsy chunkiness? Thinner tips feel just surer to aim and sloped tips assist with the illusion that tips are thin even though they may not be... So, sloped tips can be a good solution to maintain frame strength.
For me, the fatter the tips are the more of a factor sloping will be - thin profile tips don't need to be sloped but thicker frames, e.g. those that are about 3/4", is better sloped (for me anyway). If I am building a frame thicker than 1/2", I'll usually slope them.
Anyway, these are just my random thoughts on appreciating tips!
I had a typo on the word "tips" earlier... a "p" became a "t" and it made for some mind bending reading lol!
Have a good day everyone.