If someone then starts to speak more slowly, it is polite to thank them for it. The phrase mentioned above can be used to do just that. Of course, it can be used in many other situations.
A: John, could you please make the font bigger? It’s hard for me to read the words.
B: Sure! I’ll change it from size 12 to 18. How’s this?
A: Thank you. That helps a lot.