Until a situation crops up where it does... You're spending money (Ł34.99 +) on something that you do not own and cannot sell on privately.
Even if you can't, that just really doesn't bother me. I don't replay games and I don't keep anything from previous generations once I've upgraded. So while, technically, it does affect me, in practice it really doesn't.
What makes you think they will turn the servers off? A simple authentication check isn't exactly server heavy so they could keep going indefinitely for all we know. I haven't tried recently but I'm sure I could still install my disk copy of Half Life 2 from all those years ago and that needed an online check.
When this generation is just a memory I want to be able to put the games I brought into my console and be able to play them. With the XBOne you wouldn't be able to do that when the server infrastructure isn't there anymore.
A lot of people seem to be making a lot of assumptions.