Signing in now keeps you signed in for 30 days rather than a week. If you have been asked to sign in again more often than you expected, that is why.
The longer sign-in was already built and simply was not being used: when the old sign-in page was replaced earlier this month, the part that asked to be remembered went with it, and every session quietly fell back to seven days. Nothing looked wrong — you were just signed out sooner than intended.
Signing out still ends the session immediately, on every device it covers, and if you use two-step verification you are still asked for it each time you sign in afresh.