This was intended to act as a check to prevent parliament from passing constitutional amendments (which require a two-thirds majority) without the agreement of representatives from the three new states. After Singapore left Malaysia, Sabah and Sarawak were only left with 25% of the seats, as a consequence Sabah and Sarawak were not able to stop the parliament from approving laws that would encroach on the special rights granted to Sabah and Sarawak upon merger to form Malaysia.
This was intended to act as a safeguard against parliament passing constitutional amendments (which require a two-thirds majority) without the agreement of representatives from the three new states. After Singapore left Malaysia, Sabah and Sarawak were only left with 25% of the seats, resulting in their inability to prevent parliament from approving laws that would infringe upon the special rights granted to Sabah and Sarawak upon merging to form Malaysia.