[gmx-users] why not coordinates from cpt file

[gromacs query]

Hi all

I have very simple query. While continuing simulations why we need to use
*.gro (-c) with grompp as *.cpt (-t) has all the information (as checked
with gmxcheck)?
cpt file should suffice all the purposes. I tried using grompp providing -t
*.cpt file but without -c *.gro file, it does not work.

thanks
Jiom