Complex sentence: Consolidation is usually an all or nothing event-once the decision to consolidate has been made, companies are irrevocably bound, and only by having a less than 100% interest in a subsidiary, can it be left out of the consolidation.
Split into simpler sentences: Consolidation is usually an all-or-nothing event: once the decision to consolidate has been made, companies are irrevocably bound. Only by having less than a 100% interest in a subsidiary can that subsidiary be left out of the consolidation.