If you're submitting hundreds of applications, it's unlikely your'e spending hours on each application (which you probably should be)

Each resume and cover letter needs to be customized for each company. It needs to fulfil each of the roles and demonstrate compelling evidence (projects) of how you meet the requirements.

It's amazingly clear if the resume is not written for a specific job and will most likely be immediately discarded from consideration. So why bother sending all of them then?

More time on less applications leads to more interviews