Android Wear does a lot of things well, but operating with multiple devices is not one of them. If you've ever wanted to pair with a new phone or tablet, you've probably found the process pretty agonizing. Wear usually requires a reset of the watch before it will see a new device, but Android Wear BeeLink does it in a single step from your wrist.
When you open BeeLink on the watch, it will scan for nearby Android devices that are available for pairing. It shows the current phone or tablet as "paired" and lets you select any other device if you want to switch. After the watch has connected to a device, it usually remembers it and will automatically connect if there are no other connections available, but BeeLink is great for a quick swap while multiple devices are on (i.e. your phone and tablet).
Any apps on the watch that need a data connection will work fine, but if something connects to a phone app for specific functionality, it won't load properly on the watch. Re-syncing apps should make the loadout on your watch match the currently connected device, but be careful here—Android Wear can be weird about app installations.