According to those who propose the Causeway As A Transport Conduit Theory, the causeway must have been built first in order to allow easier access from a harbor to the pyramid site in the construction phase. After completion of the pyramid, the Mortuary Temple and Valley Temple were then constructed.
Proponents of the Causeway As A Processional Way Theory maintain that the causeway was used by a retinue of followers of the dead pharaoh who marched from the Valley Temple up to the Mortuary Temple where they engaged in some sort of religious observance.
The problem here is that the causeway just begins abruptly. It does not continue past the Valley Temple. There is no possible egress from the VT to the causeway. The causeway finishes at the most solid part of the VT and does not even match up with the VT ground plan. As well, the base of the VT has been excavated lower than than the causeway making any access to the causeway even more difficult.
The argument that this causeway was a Processional Way does not pass the test of logic.