The pros and cons should describe the advantages and disadvantages, which can be compared against each other. It can boil down to:
1) If this is a site in a single data center, do you want to federate? If yes, you need a multi-machine site. You can't set up active-passive environment and federate to Portal.
2) Do you have the expertise to manage a load balancer? If not, use the web adaptor. Consider that it's a single point of failure, unless you use DNS to set up redundancy.
You can look into geographic redundancy, which means you have two separate deployments, one active and one standby, and you're replicating content between the data centers.
These types of architectural discussions are a bit difficult to have via a Geonet post, as the topic can get quite complex.