4WD and AWD are similar, but they aren't the same. 4WD is much more heavy duty. AWD is meant for light duty, like snow and shallow mud. You would never take a car labeled AWD on a serious off-road excursion, it could never hold-up to the abuse.
There is a big difference between AWD and 4WD. AWD is made for driving all around constantly engaged like you were doing, however the 4WD on these vehicles is for slippery conditions only (snow, dirt, etc), because it actually tries to turn all the wheels at once, and when you go around a corner, it will bind up the drivetrain. Using this in city conditions would only be recommended if it is snowing. AWD sends power to certain wheels, and lets the others freely move so the drivetrain doesn't bind up.
Just a quick comment on 4WD and AWD. Technically they are both the same (assuming the AWD has 4 wheels!). However, the acronym AWD is usually used for what is known as a "soft-roader" as compared to an "off-roader". It usually refers to a vehicle that operates in full-time 4WD mode, using a hydraulic clutch, which does allow for some slip to cater for the differential rates of rotation of the wheels, especially when turning. AWD is set up with specific proportions of torque sent to the front and back wheels, so it really is more of a double axle drive than a true 4WD drive - you know that at least two wheels are applying power against the road surface, to drive you, whereas in an ordinary 2WD, often only one wheel is driving you, and that's the one with the least amount of grip.
4WD can (but doesn't always) come in two settings - part time and full-time. Part time 4WD literally locks up all of the wheels so that they all rotate at the same speed, regardless of the surface, so if the demand on one is different to the demand on another, one is going to slip, and if the surface isn't slippery enough, the system is going to lock up, commonly on a hard surface going around a corner.
If a part time 4WD system cannot cater (and survive without damage) for the occasional lock-up, which is inevitable when off-roading because of the variations in the surface, then it isn't worth having, but it will certainly damage even the best system if you continuously drive on a hard non-slip surface in part-time mode.
"Part time" means exactly that - you only engage it when it is needed.
Full-time, on the other hand, Even in a proper hard-core offroader, enables you to drive around in 4WD (or AWD, if you like) all the time, without causing damage, as I do in a Jeep Cherokee (Liberty) because it does allow some slip. Where I live the roads are all tarred, but there are many places where there is sand on the surface, and I prefer the extra safety and control that comes from this mode. Added to this, where I live we don't get snow, but as we only have rain for four months of the year, the first rains are accompanied by much slipping on the tar, due to the build up of oils on the surface during the dry season, so it's very useful there, too, and I drive around with amazing confidence on an otherwise hazardous surface.
I have often seen confusion in the meaning of the terms, too. "Full-time" 4WD is sometimes (incorrectly) interpreted as "hard-core" 4WD, so it is considered to be for off-road use only, but that is not the case - "full time" means it can be used all the time on any surface, whether the vehicle is equipped as a proper hard-core offroader, or simply a safe soft-roader. Believe it or not, I even struggle with this definition with my dealer!