As I understand it, the usual for most vehicles is toe in. Just a small amount, and the effect of speed is generally to reduce this nearer to parallel by utilising the slack or free play in wheel bearings and steering joints.
Specified toe out does exist, but it is very rare and I don't know the rationale behind it.
Excessive toe, either way, will lead to tyre scrub and thus greatly increased tyre wear.
Certainly as tried in my playing around, toe out on a 4/4 gives very iffy handling, with the car darting left or right at the slightest provocation. Logic would suggest this is a pretty general effect as whichever front wheel has the best grip at the time determines the direction of travel.
As many have observed, the last thing you want is for the toe to be deflection influenced as if it is, both bumps, passengers and loads will have an effect. If the toe doesn't change under these circumstances, a static adjustment should yield both predictable and unchanging results, whether you are on a hoon round a track, or taking granny home from shopping down a bumpy lane.
