Throughput is not free. Upstream services have quotas, and a batch that saturates one gets throttled or rejected, usually partway through, leaving a campaign half-finished and expensive to reconcile.
Pacing a batch is slower in theory and faster in practice.
In QXAI
Each campaign has its own audits-per-minute setting, and a batch that starts failing above a threshold pauses itself rather than burning through the rest of your balance.
Running at volume