Sodium is also used for all the electrical activity of our body (such as thinking and moving and living…), and is fundamental in adsorption of nutritions in digestion. Sodium, potassium and calcium are so important that it is difficult to even list all processes they are involved.
Edit. To add context our cells spend between 30 and 70 % of their energy to move around sodium and potassium ions en.m.wikipedia.org/wiki/Sodium–potassium_pumpA good chunk of what we eat is to move them around