The Crimson Binome
Hero
In general, you gained much more from multi-classing than you lost. A multi-class fighter/wizard was just better than a single-class fighter or wizard, in a lot of ways. Because of the exponential experience requirements, splitting your XP two ways meant that you were only about one level behind in each class compared to the single-class character, in a system that was already designed to accommodate fairly significant level gaps.Broken how?
Multi-classing also significantly diminished the impact of the one major restriction on non-human races, which was the level cap. If an elf can't get past level 10 as a fighter, but can get up to level 15 as a mage, then the multi-class elf fighter/mage gets to keep progressing past where the elf fighter stops and eventually ends up as an elf mage 15 with bonus fighter powers.
Level caps were an important balancing measure against the superior stats and special abilities of non-human races. Elves started with some powerful bonuses, but couldn't raise as high in their class of choice. Anything that let them ignore that restriction, or delay its impact beyond the scope of the campaign, was a pure power boost.