When would you use "rolling" to different strings.
I personally do not use it, I just shift my finger to the next string. Should I learn to roll properly? (My rolling-technique is quite poor) or won't it benefit me at all?

For instance, would you roll something like this (5th fret with index)? (Simple pentanonic)

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Wouldn't roll that, but if you ever want to do chorded melodies or sweeping you better learn it.
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If you have something to fret between the 5's - in this case the 7's - there's no need to roll the 5's. You could if perhaps this was an extremely fast lick, and you wanted to cut down on excess movement. Due to the shapes of arpeggios the most you'll ever need to roll though is usually 3 strings, assuming you're in standard tuning.
There's no reason to roll the pentatonic box. However, rolling is an important skill. You could try something like this to get better at it:

-1-----2-3-----4-2-----3-4-----5-----     etc.
 1 1 2 2 3 3 4 4 1 1 2 2 3 3 4 4 
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