Is it necessary to devein both sides of shrimp?
Should I remove vein from the underside of shrimp?
The vein in shrimp is entirely edible, and removing it or not is a matter of preference. That said, a dark vein can be a bit unsightly in some preparations, like boiled shrimp for shrimp cocktail, and can also add a noticeable grittiness to dishes. For this reason it's usual to devein shrimp, but it's up to you.