As a healer in ESO, it sucks not being able to cast heal while sprinting. I have let multiple teammates die because I'm trying to run towards them and heal before they get taken out. However, because i'm running, the heal never casts and I don't notice it until it's too late. Since this game focuses a lot on active dodge and reactions to game mechanics, my teammates are always running around and i'm always chasing after them trying to throw out heals. Even if casting a heal made me stop in place or slow down, that would be better than not doing anything at all when I press it during a sprint.
I also hate the random heal targeting. I admit, sometimes it's really useful just randomly pressing heal and healing the lowest guy but there's times where that really hinders the ability to heal. If one guy is at half hp and has the boss or mobs on him and it's obvious he's in the most danger and needs an immediate heal over the sorc sitting back with 25% hp, randomly giving the heal to the sorc because he's lower is going to kill this one guy. I also always try to give the tank a regen hp buff before he goes into battle but it never goes to the guy I want to give it to and I have to waste more magicka I can't afford to recast it another time or two.
So if you die and I'm the healer, sorry! I really was trying to save you.