With very large indexes, rebuilds take longer, generate more log, impact performance more while they’re running.
If you’re using high availability features like Availability Groups or database mirroring that stream the log between replicas, generating a lot of log data very quickly can create problems.
Your replica/ mirrors may fall behind. Depending on the latency between replicas, the size of the indexes rebuilt, and other operations in the database, they may be out of your Recovery Point Objective / Recovery Time objective for a long time.
In this situation, it’s particularly attractive to drip changes into the log more slowly. One of the ways to do this is to use REORGANIZE for those large indexes.
There’s a lot of nuance here, so give it a read (or watch the video).