Opener’s New Suit Rebid Doesn’t Limit His Hand Very Much

In Standard American or 2/1, opening 1 of a suit and rebidding 2 of a lower ranking suit doesn’t really limit opener’s strength very much. All we know is that opener doesn’t have enough to make a game-forcing jump shift. For example: 1H-1S-2D. Opener has 5+H, 4+D (usually), and 12-17 HCP. Responder with 9+ HCP should not pass, even with 4 Diamonds and 2 Hearts. A game might be missed.
It’s easier in systems like Precision and Polish Club, where the opening bid has a lower limit. Now it’s easier for responder to know that game isn’t there.