The CV joints, brass trunion bushings, spider and side gears and all bearings will see additional wear. The 4Runners were indeed locked at the hub end but used a disconnect on the driver's side shaft to save the diff internals, front driveline and help fuel mileage. If you think you aren't going to lose fuel mileage by adding the drag of two CV shafts, the front driveline and the differential that is immersed in cold gear oil with an already under-powered and inefficient vehicle then you are naive. It may be a negligible amount depending upon how far you drive, how fast you drive, how much you like repairing undo wear and how much those costs relate to the convenience of not taking the 30 seconds to get out and lock your hubs in.
That being said, I do drive with mine in if I know there is a high probability I will need the added traction on a trip. I will then unlock when I don't need them anymore. It should also be noted that my truck is locked in the front and causes steering issues when locked and I drive several hundred miles one way on the interstate. If you are traveling at low speeds and short distances you will probably be fine though I recommend not being lazy and saving yourself POTENTIAL repair costs.
It cost Toyota extra money to add the ability to unlock the front. They would not have done that had they not deemed it a good idea. Just my humble opinion.