I always do this. I have never unplugged a monitor and only rarely turned it off.
Standby power consumption isn't zero, but it's minimal enough that i don't consider it at all.
Is it safe? Yes.
Does it reduce lifespan? It probably prolongs it because electronics don't like being switched on and off, but this is so marginal it's not even worth considering.
Does it consume a lot of electricity? No, not a lot, but it does consume a small amount.