Do Shetland sheepdogs bark a lot?

I have a Shetland of my own. They are a very nice dog... But then it comes to the barking. As you probably know they have a piercing bark that after a while hurts! They most likely will only bark 1)When you play with them 2) When they want to get your attention 3)When a dog is barking or 4) When you have a person knocking on your door. Also as you probably know Shetlands are what you call "Watch dogs" Meaning they watch out for anything and feel like they need to protect there owners they have bonded with. When someone knocks on the door they will bark to get your attention so you are aware, think of them like your second door bell. But when you open the door, they will be fine with the person unless they don't like them of course. Tons of people will tell you the same thing " Shetlands will guide your visitors to you!" And I find that true!. To answer your more basic, they could be a big pest with there barks but end up in the end being VERY useful.