What's the point?

400 skill exp is one skill point. This value remains constant throughout the
game. If you're at a skill gap of 0 throughout the duration of the game, you'll
probably have a hard time keeping up with your skills. Even with just two
skill trees, you'll have a hard time buying everything you want, let alone
everything in the trees.

You will level up much slower while your gap is high, but on the other side, you
will also be gaining much needed SP to keep learning all your skills. With all
these skill points, you'll be able to increase all your skills at will and
reduce your skill gap as much as you like. Increasing your skill gap, on the
other hand, is much harder. Gaining levels of experience is the only way to
increase your skill gap, and at higher levels, it's much longer and more tedious
than at lower levels. If you're not bent on skill points, keep your skill gap
at zero and only buy the skills you really think you'll use. You'll level up
faster, but you'll have fewer skills to toy with. If you really like your
skills, or choose to go three (or more) trees, I'd recommend keeping your skill
gap at at least three, to double your skill point intake and allow you to use
the skills you want to use.
http://www.gamefaqs.com/computer/doswin/file/930711/43300