To be honest, I don't own anything very valuable, and I value my convenience more highly than the remote chance that somebody is going to clean out my house. Particularly since the criminal element is almost nonexistent hereabouts, and what there is tends to center on small-scale marijuana growing and dealing - although maybe that will become a problem if the heroin epidemic continues.
Locking and unlocking a door two or three times a day adds up to a considerable amount of wasted time over the course of years. Not to mention insanity like I've seen in Germany, where people lock the outer gate, lock the outer door, deadbolt the door, lock the inner door, and then roll down huge armored shutters over the windows - in an upper-middle class gated community...
Cruising house-to-house checking for unlocked cars and doors would take a prohibitive amount of time; easier to do that in suburbia, where you can cover a dozen houses on foot in five minutes.
But in NYC, I've always locked my apartment door, because it's trivially simple to follow someone into an apartment building, and not much challenge to go door to door, listen for signs of habitation, and try the door handle.
Micro-optimizations are rarely useful in terms of software development or in real life (unless you're at considerable scale which is statistically unlikely in both cases). Granted I can't know for sure how long it takes you to lock or unlock a door.
Going from my own experience locking and unlocking a door, combined, takes about 1-4 seconds depending on if I'm entering or leaving. So let's take the most (4 seconds). Let's say I unlock and lock 3 times a day (a busy day but again taking the highest numbers here). So that's 4,380 seconds (73 minutes) used per year at the maximum time. So yes it adds up but saving the 12 seconds per day wouldn't make me more productive that day (it's not like you gain that 73 minutes in a useful chunk of time) and statistically keeps myself, my family and our stuff safer.
So yeah I get the convenience factor but I don't get the whole "wasted time" piece. Certainly depending on where you live it may be unnecessary but another thing to keep in mind is there are always times for firsts (so just because your area may be historically crime free doesn't mean it'll stay that way).
Perhaps I'm just too paranoid but something so small seems fine to me :)