Throttling helps to delay the number of contacts moving through a sequence at a time and protects you from hitting your email provider's mailing limits. In addition to controlling the number of emails that go out, it ensures that the team has breathing space to follow up effectively for any response received.
Sequence throttle can be set at a global level i.e. applies across all sequences and is a 24 hour limit per user on the number of emails that can be sent out.
By default throttling is disabled.
You can enable it from Setup >> Sales Automation >> Sequences >> Throttling
Maximum throttling limit is 250 emails per 24 hours per user.