The best advantage over places that build it for you is you can get the items you really want...I’d rather have a Corsair or Coolermaster case for half the price of the Lian Li. And no one needs a Asus ROG Strix. I would get a Asrock or a non ROG Asus. You can pick the ram and power supply as well.
Those pre build places often use refurb stuff and you don’t get all the stuff the retail boxes would give you.