The National Center for Complementary and Integrative Health's cupping overview puts it plainly: "There's been some research on cupping, but most of it is of low quality," and "Cupping may help reduce pain, but the evidence for this isn't very strong." For benefits beyond pain, NCCIH concludes there isn't enough high-quality research to draw conclusions. The same source notes possible side effects including lingering discoloration and, rarely, burns or infection with poor technique or unsterilized equipment — risks managed here by using dry cupping only, conservative application and single-client equipment practices.
So why offer it? Because for some people it provides meaningful short-term comfort, it's low-risk when applied sensibly, and athletes often ask for it. You'll get it with honest framing: a comfort tool with modest evidence — never a treatment that claims to detoxify, heal injuries or replace the work of rehabilitation.