Autoscale takes maintenance mode into consideration when calculating the number of machines to keep on for multi-session delivery groups, but not for single-session delivery groups.

  The single-session delivery group doesn't account for maintenance mode because, if a machine is temporarily put into maintenance mode the scale calculations will adjust and potentially turn a machine on (or off) when that's not really what customer wants.

  This wouldn't be so much of an issue for multi-session machines since the calculation is based on load index.