I'm really pleased with the work done yesterday, and today I'll be doing some finishing touches before putting it into production. However, I won't let the client know about it :-)
This is because if they were aware of the changes, they might become influenced and start perceiving differences or believe things are slower, etc.
In reality, the performance will be improved (it's not the kind of workload where a 20 msec increase in latency would make a noticeable difference, but the modern CPUs will have a positive impact).
By keeping it quiet, they probably won't notice anything or might even appreciate the increased speed.
Sometimes, our job requires a bit of psychology too 😉