Originally Posted by mahasamatman

If you book directly from the Chase portal, you can treat your points like cash, but once you transfer to United, you lose that option.

With Mileage Plus, there is no "cash+points" option, though you can emulate it if you buy one round-trip ticket with miles and one with cash (you would not be on the same PNR), or buy two one-way tickets with miles and two with cash (you would be on the sane PNR). Another option is to buy the miles from United, though it's rarely cheaper to do it that way.