You can chose funds that are a more bond-heavy to mitigate some market risk. If you are in a low risk investment I think the odds of the the value going down over the course of 2-3 years is pretty low. Heck, even if you have to pull it out in year 3 for a minor loss, that loss is tax deductible so it's not that bad.
On the other hand if you shelve it there is a 100% chance that the money will lose value by virtue of inflation alone.
If it really is a big sum of money, I say let it grow. But basically you are betting on whether there will be a market crash / recession in the next couple years. Even then, unless you think you would need that money either to survive or to buy a house at an optimal time (assuming job prospects make sense to take on that kind of debt) you can just ride it out.