Comment by Darkstryder

To avoid something called the thundering herd problem: https://en.m.wikipedia.org/wiki/Thundering_herd_problem

For instance, a bunch of clients all make a request to a server at the same time, briefly saturating the server. If all the clients have the same timeout without jitter, they will all try again together at the same time once the timeout expires, saturating the server again and again. Jitter helps by « spreading » those clients in time, thus « diluting » the server load. The server can then process these requests without saturating.