On our coach, those plates cover(ed) the bolts that attach the inboard ends of the slide racks to the underside of the floor. The outboard ends are bolted through the floor without cover plates.
The cover plates reduce the tendency of the bolt-head holes to "telegraph" through the flooring- in our coach, it was linoleum above the plates. On the outboard ends, the holes were under linoleum and then carpet, so plates were not needed.
We just had LVT installed. The installers applied a quarter-inch underlayment. I did not watch or ask if they removed the plates before putting down the underlayment. After smoothing the joints with compound, they glued the LVT directly to the underlayment. If the racks ever need to come out, the LVT and the underlayment will have to be taken up.
2008 Holiday Rambler Admiral 30PDD (Ford F-53 chassis)
2009 Honda Fit Sport