Youthful errors, if you're not wearing protection.

And what is that supposed to mean?

The outer shape of a glyph shall have a clockwise direction whilst the inner shape must be counter-clockwise, or will not be visible (The letter O, for example, has an outer and inner shape). When both directions are reversed under straight forward application the character will still show up on screen and in print OK. But it is in-predictable what will happen when an application is used to, say, let characters overlap. Thus stick to the convention.

When the nodes of the vector that describes the glyph are incorrectly placed, like a node is on x=420 y=420, the next node is x=420 y=460, the next node id x=420 y=450 an the next node is x=420 y=470 the direction of the contour can not be established, which is a serious error.

Ok, so unless you let the characters overlap, it won't usually be a problem, right?

I see, it doesn't make much sense to do things like this, so a serious error, ok, but how will this affect the "regular" user?

in-predictable

Can this please be a less "global" answer? I'm really interested in trying to understand the consequences of these problems.

Sorry Fred, that was not a global answer but the only possible answer. You can not tell on forehand what is going to happen as it completely depends on the application used to use the font. Sometimes you see nothing, sometimes you get weird effects. Most times only with large sizes. And as it is that simple to do things right, why not?