Sefer Tiferes Shlomo explains that this night has the power to provide protection for every night of the year. The word “shimurim” (literally “protections”) is written in the plural to indicate that it refers to every night of the year.
The Sefas Emes (Pesach 5652) writes that the protection of the night of Pesach remains throughout the year and lasts until today. He adds that the reason we put aside a piece of the Afikoman is to symbolize that a piece of that protection is set aside to last eternally.