"Rule of Three" for GURPS Magic

The "Rule of Three" is a houserule for magic that has been working quite well.  The original goal was to eliminate skill 15 as a breakpoint for reduced energy cost, and instead assess a skill penalty for casting magic "on the cheap".  It really took off when I realized how nice it is to have the same penalty (-3) for all sorts of things - no more looking up penalties!

Rule of Three for spellcasting: -3 to spell skill for each:

• Halving of casting time (round up, minimum 1 second),
• Reduction of energy required by 1,
• Casting without chanting, or
• Casting without arcane gestures.

Note that spell resistance and chance of critical failure are based on adjusted spell skill!

Spell maintenance is normally at full energy cost, which requires no further rolls.  If reduced cost is desired, the mage can re-roll the spell skill at -3 per point of energy reduced.  This must be repeated for every maintenance cycle where reduced cost is desired.

Effects in play:  This has allowed for more varied character builds, since optimizing for skill-15 with 1 pt in the spell is no longer necessary.  Resisted spells are typically cast at full energy cost, while utility spells are almost always cast as cheaply as possible - this does make the rolls a little more interesting, since players like to drop skill low enough to save energy, but high enough that they'll probably make the roll and not waste 1 FP.