A lot of times you will send a (possibly large) blob of text repeatedly with a few minor changes.

One example I've used in practice is session descriptions (SDP) for WebRTC. Any time you add/remove/change a stream, you have to renegotiate the session, and this is done by passing an SDP blob that describes all of the streams in a session in and out of the Javascript Session Establishment Protocol (JSEP) API on both sides of the connection. A video conference with dozens of participants each with separate audio and video streams joining one at a time might require exchanging hundreds or even thousands of SDP messages, and in large sessions these can grow to be hundreds of kB each, even though only a tiny portion of the SDP changes each time.

Now, you could do a lot of work to parse the SDP locally, figure out exactly what changed, send just that difference to the other side, and have it be smart enough to patch its local idea of the current SDP with that difference to feed into JSEP, test it on every possible browser, make it robust to future changes in the SDP the browser will generate, etc.

OR

You could just send each SDP message compressed using the last SDP you sent as the initial dictionary. It will compress really well. Even using gzip with the first ~31 kB of the previous SDP will get you in the neighborhood of 200:1 compression[0]. Now your several-hundred kB SDP fits in a single MTU.

I'm sure WebRTC is not the only place you will encounter this kind of pattern.

[0] Not that either gzip or using part of a document as a dictionary are supported by this draft.