Shims

What are the point of shims? I might buy some for my dark magic if they are useful. ???

they are placed in the bearing seat of the yoyo to elevate the bearing and increase the size of the gap. it is also used to create a fixed gap or somewhat fixed

as for being usefull, they can be if you feel that your gap isnt quite wide enough but if you think its fine the way it is I wouldnt put them on the top of your list. I got some for my DM ant I ended up losing the the two I bought but it plays fine without them. Buy some to experiment and see if you like them theyre not that expensive just be careful pulling your yoyo apart on carpet ;).