In jmeter, i am observing an increase in response time when i add a constant timer in JMeter, and i am expected that adding a timer (sleep) would reduce the response time and make it faster. I added timer to make delay before every http request call
for ex httpreq1- with timer is taking - 875ms and without timer 267ms
i have added constant timer at thread group level
Adding timer will improve response times only in the case when the system under test is overloaded.
When you're adding a Timer you're basically decreasing the throughput (number of requests per second) and it's more "easy" for the system under test to handle the load.
If you haven't reached the system's saturation point or bottleneck adding the timer will not have any impact apart from decreasing the number of hits per second.
In general it's highly recommended to have timers as real users don't hammer the system under test non-stop and they need some time to "think" between operations. So it worth having timers with reasonable and realistic think times along with other actions you need to take to make JMeter to behave like a real browser