Found 5.8mm non obstructing kidney stone incidentally on ultrasound. urologist said it is up to me whether i want to leave it because its not causing issues or have ureteroscopy. is there a benefit to having it removed?

If the stone is successfully removed, you can avoid complications even stone doesn't move or when it moves down then it is stuck because the stone is bigger than 5 mm. However, the retrograde approach (ureteroscopy) for stone removal isn't simple and not always successful which depends on the stone location and urologist's expertise. Leave it for now if stone is in the low pole & asymptomatic.

Yes. A ureteral stone can cause a painful colic if it moves in the ureter. If can also cause obstruction to the flow of urine and damage the kidney. It would be prudent to get it removed. Talk to your doctor if lithotripsy is an option, as that will avoid an invasive procedure.