What's the point of locking doors?
If a criminal wants to get in to your house, he's going to get in regardless of whether you keep your doors and windows locked or leave them open.
Now, if you're home, it makes even less sense to lock your doors...during waking hours, though. If the criminal knows people are there, they are less likely to want to rob you (during the day). During the night (when you're sleeping), however, it does make sense to lock your doors. Having locked doors while you are sleeping allows you to hear them break in...which will give you enough time to wake yourself and get a weapon ready to face the intruder (or hide and call the cops). If you're not home, you can either lock or not lock the doors...but the criminal will get in regardless of whether you lock them or not.
Now, if you have a car, you should never really lock your car doors. Your windows will just get smashed if they want in. So, keep it unlocked unless you don't care about the damage.
As a side note: This would be a perfect topic to add a poll. People may be more inclined to repspond if they can do so anonymously.
Edit: Now, if you have suspicion or have a high risk of someone coming in to your home, while you are there, then
.yes, lock your doors. As when you are asleep, that will give you some time to prepare to defend yourself. However, If you are not at risk of facing an attacker, at any moment, no point locking the doors.