Should you roll it over? Maybe. Unless your former employer requires that you remove the fund (most do not), there is no reason to do so unless the employer's investment offerings are limited, expensive or performing poorly. Rolling funds over into an IRA (you should never, ever, ever, ever cash them out or withdraw them. NEVER) may trigger tax penalties and additional fees from the employer to the receiving institution. So in deciding whether to roll them over, you should review your returns on investment for the past 3-5 years. You should review the expense ratios of the funds and you should examine the level of diversification that the employer is offering. (Leaving a job is always a good time to look over the portfolio and rebalance anyway). If there is no reason to move the funds and you're relatively satisfied with the investments, leave them alone. Remember that while you won't be able to contribute to that account any longer, if you continue to reinvest those dividends and monitor to make sure the account stays balanced, you'll accumulate one more retirement stash! This is a pool of investments that you wouldn't otherwise have access to so unless you determine that they are bad investments - consider leaving them where they sit.
Now one more thing...I don't give investment advice...I'm an investment educator. My objective to simplify finances and provide context for financial decision making. So don't go tell the people I told you to leave your money in a hole in the ground. What I'm saying is that despite what we've been taught, you don't have to withdraw money from your retirement accounts and you should investigate it before you do it.