IPR is an important tool that is required to create space when correcting crowding.
However it is not absolute. Teeth do not move exactly as we like and depending on aligner manufacturer they may round up the space required.
As a general rule it is better to do ipr incrementally. It is also better to routinely check with ipr strips to ensure no binding interproximally even when no ipr is due. Premature binding leeds to poor tracking outcomes also.