Not true. NormalCheckers do many useful things on the ChessSide, including blocking check, plugging PawnDrops, and clogging the center of the board. Granted, a NormalChecker is much less valuable on the ChessSide on than a pawn, but you still don't want to lose them, because they can be extremely powerful on the CheckersSide.
They make extremely good blockers when your opponent successfully promotes following a PawnDrop and you've left your King behind a protective wall of pawns with no Luft. Additionally, if there are NormalCheckers already in place in the Center and you start a mating attack, they make good support pieces (as the protection cannot be blocked as easily as can a NormalChecker check).