From memory you cant use the account services tied in with your live account, cant change backgrounds / customization, and you get a watermark saying its unactivated.  If you want to activate it without paying you can always join the insider program fast track.. That reactivates every 90 days from memory.   

I had a legit key that I installed into my virtual machine. Suddenly it became not activated (I rolled back/restored the VM a few times here and there).

Everytyhing still works. To my surprise.

Much more satisfactory to get it activated. Assuming your licence is kosher, you should ring Microsoft to get it activated.

linw:

 

Much more satisfactory to get it activated. Assuming your licence is kosher, you should ring Microsoft to get it activated.

 

Satisfactory? Why? What's the difference? 

I ran it unlicensed for a while, was fine apart from what askleon mentioned. Machine was on 24/7 and never rebooted etc.

Dulouz:

 

linw:

 

Much more satisfactory to get it activated. Assuming your licence is kosher, you should ring Microsoft to get it activated.

 

 

Satisfactory? Why? What's the difference? 

 

If you have paid for it as you should have why would you not gain full control over it. 

Dulouz:

 

I'm running an unactivated version of Windows 10 on my MBP. Are there any issues that this could cause?

 

MS could just decide to sent out an update that kills off/restricts unactivated Win10's
Im surprised they haven't already