All my weapons that are loaded, have a round in the chamber with the exception of my Remington 870 Shotgun. I was informed by a good friend that they have been known to discharge when dropped on the stock.
You should carry how you feel comfortable. The time it takes you to rack the slide could make the difference. One of the main points of a GLOCK is that there are no external safeties and switches, etc to manipulate when you need it. Draw the weapon, identify target, point and pull the trigger. Racking the slide adds an additional step in the mix. If you do decide that this is the way you want to continue carrying, you should practice constantly on drawing the weapon, racking the slide and then getting on target. Of course, practice with an EMPTY WEAPON!!! Remove the mag so the slide will drop free while practicing.