Throttling (or pacing) is the deliberate limiting of a campaign's send rate, in messages per minute or spread over hours, so that replies, calls and clicks arrive at a pace the receiving side can absorb.
Sending as fast as possible is rarely the goal. A promotion that produces a two percent reply rate at 400 messages a minute generates eight conversations a minute; a link that sends a thousand people a second to one landing page tests the server more than the offer. Pacing spreads the send and, combined with local windows, keeps it inside acceptable hours.
Pacing also protects routes: a sudden spike on a new destination looks like spam to operators.
At SMSMeteor: a campaign or a batch takes pace.per_minute or pace.over_hours; pause and resume are instant.