Is it safe to blend ice using a blender?

hi, a lot of smoothie recipes that i come across tend to say 'blend ice'. i was wondering if this is safe, wont the blades get ruined? and if i dont dont do this, what will happen?
thanks
Update: i meant to say if i dont add ice to the recipe, what will happen to the smoothie? also instead of blending it, can i just place crushed ice?
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