We have just upgraded to latest version of Octopus. Our previous version (3.8) had no machine limits and we never thought about it, but our new license has limits that covers the amount of machines we want to deploy to - with some growth allowed.
However, once per quarter we like to rebuild all our VMs and phase out the old. For (relatively) short periods (1 week) we double up on the number of VMs. We can see that with the new machine limit, this is going to get messy - although it would be a lot less messier if disabled tentacles did not count.