In an online services company, a perf team can be net profitable rather than a "cost center." The one at my work routinely finds quantifiable savings that more than justify their cost.

There will be huge mistakes occasionally, but mostly it is death by a thousand cuts -- it's easy to commit a 0.1% regression here or there, and there are hundreds of other engineers per performance engineer. Clawing back those 0.1% losses a couple times per week over a large deployed fleet is worthwhile.