I think the point is that one can only devote a finite amount of time and energy searching for a job each day before they hit diminishing returns, due to both mental fatigue and physical limitations. Though as another commenter pointed out, volunteer work is a common resume-building and networking tactic.
The poster above you is making a comparison between working a job and finding a job.
Working a job: you spend 8-12 hours at the job and then spend your leisure time doing other things, like studying or meeting friends or watching tv.
Finding a job: you spend 8-12 hours trying to find a job, and then you spend your leisure time doing other things, like volunteering.
The question you posed earlier was, why wouldn't someone just spend all available time (let's say 16 hours per day) trying to find a job, instead of doing anything else, like volunteering. The poster above you was responding to that, trying to demonstrate how the same suggestion would be ridiculous in the context of working a job, and it should be equally ridiculous in the context of finding a job.
