It would be bad in that it makes employees' stock less liquid. Stock-based compensation is a huge part of many employees' comp packages.

I think a small subset of people might adopt a short-term approach to equity ownership. I think a much larger subset would simply be selling to access the money they rightfully earned or to diversify their holdings instead of having the bulk of their stock portfolio in a single company.

What if someone froze half of your paycheck and said you can't touch it except for the two months out of the year that they say you can?