With standard 802.11 roaming, you have to reassociate and reauthenticate to the new AP. While this process is underway, you can't pass any traffic. For open networks or simple auth schemes like WPA2 single-password, this isn't very noticeable; however, for heavier-weight auth schemes like 802.1x this pause is substantial and is especially noticeable on voice/video calls. 802.11r is a scheme for caching the authentication info, letting you avoid the 802.1x round-trip to a central auth server.
For a 5-AP network, usually with shared-password WPA2, it's not necessary.
With standard 802.11 roaming, you have to reassociate and reauthenticate to the new AP. While this process is underway, you can't pass any traffic. For open networks or simple auth schemes like WPA2 single-password, this isn't very noticeable; however, for heavier-weight auth schemes like 802.1x this pause is substantial and is especially noticeable on voice/video calls. 802.11r is a scheme for caching the authentication info, letting you avoid the 802.1x round-trip to a central auth server.
For a 5-AP network, usually with shared-password WPA2, it's not necessary.