I never thought I'd see this title for a thread on here. Kudos! Its a great question that shoulda been asked before...just don't recall ever seeing it. Usually, its the opposite, 'Is HS ball a necessity?'
My short answer is 'no, not a necessity' but in general its a good idea. Our older son was gonna get recruited whether he played travel ball or not, but it sure increased his opportunities. Our younger son was gonna get recruited by at least someone local, but travel ball together with having a nationally recognized HS coach in a nationally recognized HS program widened his visibility too. Bottom line, in his case he had both a HS coach and a well respected travel coach in his corner - it helped. No doubt about it.
High quality travel ball is a place to be seen with and against other high quality players. More scouts/coaches show up to these games. It increases the 'touch points' and thus the opportunities. But maybe you and your son are happy with University-X which is just down the street?
And they are right above, you could grab the attention of more coaches by doing a couple well targeted showcases too.
You need to figure out what situation your son is in, you are in (financially, family obligations, targeted schools) and create and execute a plan.