Let us say we have 3 requests in a Thread group and we have a listener and see the results. If we run this thread group the 3 request will run only once.

If we increase the number of users to 3 then all 3 requests will run 3 times and there will be no order.

If we keep the number of users 1 but increase the number of loop counts to 3 then again all 3 requests will be run but there will be order i.e req1 ,then req2,req3 as user is only 1.

Now if number of users is 1 but loop count is 3 but we want some req to only run once like if it is a login req or logout req add a Once Only controller and add that particular request as child to that controller.

After that if we run the thread group we see that request has only run once no matter what the loop count is .