Lane isolation separates traffic classes, most commonly transactional versus marketing, onto distinct sending domains, IP pools, and queues, so a reputation event on one lane (a bad marketing send, a compromised customer account) doesn't throttle or block the other.
Without isolation, a single high-complaint marketing campaign can delay or degrade delivery of password resets and receipts sharing the same sending identity, which is a materially worse failure mode than the marketing send itself underperforming.
PulsePigeon enforces lane isolation as a platform-level default rather than an opt-in configuration, precisely because the cost of getting this wrong (a blocked password reset) is asymmetric with the cost of a delayed newsletter.