My doors are never locked when I'm at home-in the summer, but in the winter they most likely are probably because I don't have the doors open to get air..
My back sliding glass door is always open, screen door closed, but not locked. I have 2 kids going in and out all the time.
Front door is wide open, screen door closed.
I don't think locking the screen door would be much of a deterrent. LOL
But the front one is locked because some salesman was walking up and down the street, so it just made me a little leery.
My FIL(lives upstairs in his 2 family, we live on the first floor) locks the front door constantly, it drives me insane!
I will run out to get the kids from school or from Rec in the summer, literrally a block away. If he leaves in the 5 minutes I'm gone, the door is locked when I get back.

We have a big, loud dog. No one is going to come in...and if they try, they will get a very unpleasant surprise.
So now everytime I go out for a couple of minutes, I leave the back door unlocked.
When I go out grocery shopping or something where I'll be gone for a while, I do lock the doors.
At night, everything is locked, doors and windows, alarm on.
But..for those of you who have your house locked all the time, are your windows also locked? I like to get the fresh air in whenever I can!
Growing up the only time our door was locked was at night or if everyone in the house was not at home.