This is the maximum number of paths with equal routing metric value that the router is permitted to split traffic between, and it follows the replaceOnlyWhileDisabled behavior. It caps how many equal-cost paths (ECMP) IS-IS will actually install when SPF finds multiple best paths with the same metric, so setting it to 1 forces strict single-path routing even when redundant equal-cost links exist. For example, setting this to 4 on a router with 6 equal-cost uplinks to the core would still only use 4 of them for any given destination, leaving 2 links' capacity for that destination unused.