Some agreements don't need a lengthy confirmation — just two words that say it all. Say less captures exactly that instant, no-explanation-needed agreement in a quick, efficient texting phrase.
What this phrase actually communicates
This phrase signals instant agreement or understanding, indicating you've heard enough to be fully on board without needing any further explanation or convincing from whoever proposed the idea or plan.
Efficiency as the entire point
Rather than typing out a full confirmation message, this short phrase instantly conveys complete understanding and agreement, cutting straight to the point without any unnecessary elaboration or back-and-forth clarification.
When this phrase typically gets used
This phrase is commonly used when someone proposes a plan or idea that you're immediately on board with, signaling you're already fully convinced and there's genuinely no need for any further persuasion or discussion. 
A man in a car with a surprised look on his face says " my reaction to that information... — view on SoundGIFs
Signaling trust and quick decisiveness
Using this phrase often implies a level of trust in whoever made the suggestion — you're confident enough in the idea, or in them, that you don't need additional details before agreeing.
Occasionally used with a sarcastic edge
This phrase can occasionally be used with a slightly sarcastic edge, implying someone has already said more than strictly necessary to make their point, though its primary and far more common use remains genuine, enthusiastic agreement.
Similar quick-agreement slang
This phrase sits alongside other efficient texting slang, similar in spirit to how what does it's giving mean in slang condenses a more elaborate thought into a short, easily understood phrase.
Conclusion
Say less gives quick, genuine agreement its own efficient, no-explanation-needed texting phrase. For more slang and texting phrases explained clearly, browse SoundGIFs' full News section.