There's popular series on youtube (Troy Grady, Cracking the Code) devoted to pick slanting. The main idea is to avoid getting your pick 'caught' between strings. Does Tomo have an opinion?
Here is Tomo's comment:
"Thanks so much for subscribing to my Guitar Wisdom. I have not seen those YouTube videos, so I cannot comment on them. I teach alternate picking technique in many Guitar Wisdom lessons, especially in the Sight-Reading Series. When you practice, you should play with 1) enough volume and 2) more treble than bass, so that you can hear whether you are using good picking technique."
Nettle
I think the pick slanting really only applies to speed picking. I use it only when playing very fast to not get the pick stuck and cross to the next string.
Nettle