I always do this even though my mare is super wonderful with needles. I give Legend (IV) so it’s extra-important that she stand still. I always feel terrible if I don’t get it the first time, and I find a fresh, sharp needle makes it easier for me. Slides in nicer. I also struggle sometimes to get all the Legend out of the bottle (that stuff is $100 a dose, I want to get it all!) so I can pull out and reinsert for a new angle in the bottle and know that I’m putting a fresh needle on anyway, so I don’t have to worry about it being dull.
It could honestly be a bit of a mental thing with me, once I ran out and only had one needle left and I could not find the vein to save my life because I kept telling myself I only had one shot at it and the needle was already a bit dull from drawing up. It just makes me feel better about jabbing them when I know it is sharp.