What can you and can't you do with an apple watch that has activation lock
To answer your first question: There are no limitations to having Activation Lock enabled on your Apple Watch, except for:

With Activation Lock, your Apple ID and password will be required before anyone can:

unpair your Apple Watch from your iPhone,

or pair and use your Apple Watch with a new iPhone.



– the above taken from Apple's support site –
But I don't know if those are considered disadvantages.
As for your second question, you can unpair the Watch from the iPhone by:

Launching the Settings app on your Watch
Select General
Tap Reset
Tap Erase All Content and Settings
Enter your password, if needed
Hit Continue