Purpose of .gro file type?

May i know what is the function of having .gro file types as output?
For example, if i run pdb2gmx i can specify either .pdb or .gro. What is the advantage of choosing .gro if my software can view .pdb files directly as a visual model but not .gro file types?

For subsequent steps such as EM, equil, production, can .pdb be used throughout instead of .gro?

It’s an old GROMOS file format. Simple and compact. You can use whatever format you prefer.

nice! thanks Justin