Blood is definitely an interesting and complex fluid. It has a very distinct smell and taste that does change with age as your liver and kidneys lose efficiency. I know the taste from biting my tongue on accident and busting my teeth when I was a kid... I actually jumped once and went face down in the dirt and my front teeth went through the skin just below my bottom lip. I had to have stitches above my chin and they had to stabilize my front teeth that were loose from the event....so I tasted blood for about a week. Everything tasted metallic to me.
I don't work in healthcare, but I'm sure some people could tell you a lot about how different peoples' blood smells based on age/diet/etc...
I've only been witness to a few instances where I saw someone free bleeding out of a massive wound that needed to be sutured on the spot to slow the bleeding. During those events, I basically came to terms with what I was witnessing and realized that even though it wasn't normal, the goal was to stop the bleeding before the person needed a unit of blood to recover. We worked quick enough that they were just week for a few days, but needed no additional blood (despite losing a ton). In cases like that, you really need a mask if you're squeamish.