Picture a piano part: treble clef on top, bass clef below.
The C clef identifies Middle C. (between the 2 clefs)
The C clef can move around on the staff.
A C clef on the 4th line(from below) would enable the player to read
more low notes on staff lines without using ledger lines.
A C clef on the lower lines enables the player to read higher notes on the clef without using ledger lines.
Typically in instruments, bassoons & trombones & euphoniums & horns use a C clef to replace high ledger line notes. In singing, the alto & tenor voices may use the alto & tenor (C)clef.
It gets difficult reading a series of notes which have 4-5-6 ledger lines.