Should you stay signed in?
It's easier in the short term but it could put your security at risk. It's tempting to remain logged in to your favorite websites on your smartphone, tablet, or laptop. But if you're using a public computer or WiFi connection, that's bad idea.
What does stay signed in do?
When logging in from the website's main page, you can stay signed in from the next time you access the page by clicking "Stay signed in". (This function uses cookies.) By doing this, you can conveniently stay signed in without having to enter your login ID and password each time.
Why do websites want you to stay signed in?
Other websites may forcibly sign you out after a hack or other data breach, just to ensure all their users change their passwords and are legitimately signed in. Even if there's no problem, many websites force you to sign in when accessing potentially secure data.