The risk with leaving your investments in an old account is that you may not have as many investment options as you would if you transferred it to an IRA. For example, they may only have investment options with slow growth, high fees, or investments you don't agree with (i.e., oil drilling). When you transfer your funds to your own account, say with Vanguard, you have full control over what you invest in (and the fees associated with it). You could have a much better retirement account (i.e., mutual funds, index funds, etc.) suited to your financial goals when you transfer it. Yet mainly, the main reason you don't want to leave an old account behind is that you may forget about it, or the company may go under, making it difficult for you to get your funds after the fact. Besides, when you initiate a transfer with Beagle, they can help you with it, making it much less intimidating.