If your shooting in your glutes and quads, good luck on hitting a major artery or blood vessel for that matter. If your good at shooting in the proper areas, the chances of hitting anything is so minimal. If you're spot injecting, especially in the chest and biceps, it's very important to aspirate, 'cause those muscles are smaller and you have a higher chance of hitting something. Although, the chances of you actually getting the pin directly into the vein or artery are minimal, it's likely you'd pass right through it. I work as an RN in a psychiatric clinic and give hundreds upon hundreds of injections every year and NEVER aspirate. It actually is not necessary and is actually an OLD practice. There's nothing wrong with it, but it is not necessary.