Although not fun to think about, beneficiary designations are a critical part of retirement planning. After all, since everyone eventually departs the planet, beneficiary designations will eventually be implemented. Don't assume your will shall guide the distribution of your assets. In fact, when it comes to retirement plan accounts, your will typically has no bearing at all. Consequently, it behooves you to periodically check what you custodian has for you on file for your beneficiary designation.
Even other assets, such as your home, may pass outside your will. That's why your ownership status also matters. Common ownership statuses include tenants in common, tenants by the entirety, and joint tenancy with right of survivorship (JTWROS). When you own an asset in either of the last two manners, it won't matter what your will says.