What is SGOV and why does it “reset” every month

Why does SGOV reset at the beginning of each month?

Do people buy at the start of each month the and sell at the end before it drops back down?

I have seen post on other subreddits and other apps where people have hundreds of thousands of dollars in it. Generally are they buying and selling every month or just letting it ride?

Is it smart to buy and sell it every month?