Example of using Failover
I do not understand this lines : A common practice for a two-WAN setup is to make three gateway groups for a multi-wan configuration: one that load balances, and two for failover, one preferring each WAN. This could be expanded for any number of WANs: Make one group that prefers each of them and fails over to some ordering of other WANs. This will allow selectively putting traffic on each WAN as well as load balancing. in https://www.netgate.com/docs/pfsense/routing/multi-wan.html. For example, 3 rules resides in firewall, at the top rule in which using balancing beetween two WAN interfaces and two with failover.
balancing - wan1 wan2 both Tier-1
failover1 - wan1 has TIer-1 , wan2 - Tier-2
failover2 - wan2 has TIer-1 , wan1 - Tier-2
When traffic goes throught the firewall what is happened for my view :
it meets rule at top balancing will using every time never reach second rule.
How balancing works - When two gateways are on the same tier, they will load balance. This means that on a per-connection basis, connections are routed over each WAN in a round-robin manner. If any gateway on the same tier goes down, it is removed from use and the other gateways on the tier continue to operate normally.
Why i should using two other failover rules if balancing do it for me
This is to have all possible combinations just in place if you need them.
I can recommend the Multi WAN Hangout: https://www.youtube.com/watch?v=svZ6PKqGdtg
Very good walk through and explanation as always done by @jimp :-)