Originally Posted by
RoadLight
But you have to remember that most 1x drivetrains also use a wider range of sprockets on their cassette. This removes some of the 1x advantage regarding chain length and a single chainring.
OP is running an 11-speed XT which has a 42T capacity in the shortest (medium) cage version. Running an 11-40 cassette with a single chainring uses 29T of capacity leaving an additional 13T (6.5 inches) of chain the RD can take up. So adding a couple inches to the big-big+1 length is guaranteed to work fine with no negative effects (other than four links of added weight). This is exactly what I do on my 1x10 CX bike -- X7 short cage RD (30T capacity), 11-32 cassette, 4.5" excess capacity, chain sized big-big+3" allows me to bump the cassette up to a 36T max or the chainring to a 44T max without touching the chain.
No 11-speed chain that I know of has reusable pins, so lengthening an 11-speed chain after breaking is always going to require an additional master link (or Shimano connecting pin). No real harm in doing that, but no real advantage either when you can just leave a little extra on the chain in the first place.