A typical groom's tuxedo rental — jacket, pants, shirt, vest, tie, shoes, accessories — runs around $200.
Book a wedding party of five (the groom plus four others), and that $200 disappears. The groom pays nothing for his look.
Add ring-bearers and they get 25% off their attire — usually saves another $30–$50 per kid.
For a typical wedding party of 6–8 plus a couple of ring-bearers, the savings add up to $250–$350 versus paying for everything individually.