I don't see any reason why having a toe in or toe out setting to your tyre should provide any effect at all to the drive.
It almost feels as if it should add to the cons when driving along a straight road!
Wouldn't a toe in configuration for example, mean that when moving forward, both wheels tend to move in an oblique manner and not the straight manner in which we intend to drive along?
In the vehicles I have the most experience with, the best toe setting is "0" which is where both wheels are parallel, and provide minimum rolling resistance.
The alignment straight ahead is commonly called static alignment. Various toe changing schemes are employed to aid in cornering, and also with differing suspension heights. In general, some toe-in helps maintain directional stability, and some toe-out aids in initiating turns and taken to excess could impair directional stability.
When tires scrub, or work against each other, the tire wear is increased, and the directional control may be affected by pavement differences.
There are numerous well written descriptions of toe on the web. Some of the racing sites or rally sites have nice graphics and good explanations.
Toe-in is to compensate for the natural play in the steering / suspension system on a non-front wheel drive car - it then allows the wheels to track parallel. Toe-out is for a front or four wheel drive car to counter the effect of the driving force "pulling" the wheels forward. This is also coupled with the Ackerman steering angle when cornering as the inner wheel needs a greater angle than the outer wheel.
If you had a perfectly-straight set of wheels, you'd find they would still swerve off to a certain side after a while. That's why you have to make micro-adjustments on the steering wheel. If they were perfectly straight, you'd A) struggle to turn the wheel if on an un-assisted steering rack and B) you'd be making more frequent and more prominent adjustments with the steering wheel whilst driving.
If you ever had one of those little toy cars that you could pull back, let go, and then have it launch off, you'd notice they would never go in a straight line (which always annoyed me because I loved trying to get it to go between little lego buildings I used to build as a kid) and would find itself somewhere else to where I wanted. You'll also notice that if you drive down a road with a 'pitch', where the centreline is ever-so-slightly higher than the edges of the road, your steering wheel tends to swing to the side of the road. Yes, this is normal, but if you're holding onto the wheel, it's almost unnoticeable. If you had perfectly straight wheels, you're going to be physically fighting the wheel to stay straight when you're going over 15-20mph.
No, I don't have any technical data to back up this, but I've had plenty of time experimenting with cars to find different set-ups, and also helps me diagnose some problems with steering when you've seen what effects are caused by what firsthand.
All examples are considering vehicle is traveling forwards. First I'll start with a front-wheel drive vehicle. Upon any acceleration/ torque the front tires try to toe in. This is a natural force, but since there are so many moving steering/suspension parts on the front, some "play" has to exist. When these cars were first coming on the scene, manufacturers gave a specification for toe OUT of approx. 3/16". They later changed that spec. to "0" or 1/32in. IN or OUT. The reason being once the vehicle reaches highway speeds on flat surfaces, very little acceleration/ torque is on the wheels. It becomes more like a rear-wheel drive vehicle which has NO drivetrain torque on the front. Here the force on the tire (front suspension) is from contact friction with the road surface. In the case of rear-wheel drive, the front tires always "want" to toe out as speed (friction) increases. Sitting stationary on an alignment rack they are adjusted slightly toed IN 1/16in. - 1/8in. usually. If adjustment on either is out of spec.'s in excess, it causes tire wear and poorer fuel mileage (snow-plow). If toed-out too much the vehicle tends to "wander" and small turns are easy (little effort). If toed-in too much the vehicle has very "stable" driving and turns are more difficult.
