What use does the switch filtering function serve?

on paper please

NAND2TETRIS HARDWARE SIMULATOR HiLoMux - This has one 8-bit input bus, in, and one 4-bit output bus, out. Alsopresent is a sel input, which is used to select what appears on out. Ifsel is false, then out should contain the lower 4-bits of in (i.e. in[0],in[1], in[2], in[3]). If sel is true, then out should contain theupper 4-bits of in (i.e. in[4] mapped to out[0], in[5], mapped toout[1], etc.). In other words, the HiLoMux can be used to select anibble from a byte please use the skeleton program below CHIP HiLoMux{    IN in[8], sel;    OUT out[4]; PARTS:     }

I wrote out this circuit but need help to implement it into the two 7 segment displays