Living in the present is ideal and usually very difficult for most people to achieve. And, yes, it is extremely beneficial to happiness.
Being present is a form of meditation in and of itself. One way to practice “being present” is to take improv classes, read books about improv, and to practice improv with a group. The reason, you cannot perform improv effectively without being in the present.
When performing improv you must be present to understand where things are going, what was said, how to interpret it, and respond accordingly. When we are thinking about the past or the future, we might miss something very important in the now.
We expect much of ourselves because of society, parents, coworkers, and more. When we don’t meet an expectation, we get upset. That’s the only reason we get upset. Expectations not being met.
By staying present, you can see the expectations you had for yourself and act accordingly so you can avoid being upset. There is actually a flow chart for stopping yourself (in the present) from being upset.