It hurts your ability to rebalance efficiently, and makes things more complicated than is necessary. Additionally, if you're at a fund company with different s

It hurts your ability to rebalance efficiently, and makes things more complicated than is necessary. Additionally, if you're at a fund company with different share classes based on balance, you also get higher expenses by dividing things up too much. Eg Vanguard's Admiral shares reward you with a lower expense ratio for having more money in a given fund, since it lowers their own overhead.