ADDITION NOTE: I am talking about moving funds WITHIN the 401k

My opinion:

When working with an employer-matched 401k, there are certain very strict limitations on the amount of times you can move funds within a given time period.

I believe most 401ks have a limit set that funds being moved OUT of a given fund cannot be moved INTO the same fund within the same month or quarter. You have to read the exact rules. This is done to discourage speculation with retirement annuities.

Just remember that if you feel like either cashing in or out of the market at any time, and you cash into a volatile, high-risk fund, you will not be able to move the funds back into the fund you moved the funds out of - hence you should make sure that your choice of funds includes multiple low-risk, stable annuities that you can move your funds into should you make a mistake.