I hope you're doing well. Orphans have a few advantages, for one you are removing less copper from the board. In situations of high mechanical and thermal stress this can avoid warping in the substrate because the copper is more uniformly spread on the surfaces of the board. Having the extra copper can give a slight advantage for heat dissipation, again because of copper uniformity on the surfaces.
With that said, vzoole is correct. Unconnected copper pours can behave like unintended antennas so it's best to avoid them if you have high frequency circuitry. For your basic arduino project it doesn't matter much either way. These things become problematic when you are working with high frequencies or high power.