You should be okay with what you have. Depending on the type of flange (plastic, cast iron, etc.), keep in mind that while the flange itself may not move, it is weakest where the T-slots are for the closet bolts. While the flange may not move, depending on the strength of the flange itself, not having the rim anchored may risk breaking it. Normally, this would only occur if you overtightend the bolts while mounting, or if it got knocked, say if someone fell against it. Depending on the material, that kind of a thing may not matter one way or the other.
One of the pros that sees maybe hundreds or thousands of these things in a career will have some better insight.