Display Normals

If you don't render to a target that supports the full float range than yes, your values get clamped to [0, 1]. So you would have to transform them to that range beforehand (value + 1 / 2).

If you try to display all three colors at once it can be very difficult to
interpret what information is being conveyed.

I have found it useful in the past to display a single direction at a time when debugging. This lets you clearly see the directionality of the surface normal, and if you set things up to switch the axis that it displays to change every 1-2 seconds, then you get a very good picture of what is going on.