Sales negotiation
After sending a proposal, the salesperson does not follow up for several days; the prospect, who was hesitating, ends up writing of their own accord, worried about losing the slot or the discount announced as temporary.
Let the silence work after a time-limited offer, rather than following up too soon and betraying your need to close.
Silence puts the ball back in their court and avoids looking needy; it brings out the client's real motivation.
Too long, and it pushes the prospect towards a more responsive competitor, without your ever knowing.