It did two things:
1) It showed that Saul was far more instrumental to the events that played out in Breaking Bad than we previously known watching the show. Essentially, the entire destruction of Fring's empire and then later Walt himself is tied to Saul not listening to Mike and leaving it alone. That's actually pretty interesting and insightful
2) Narratively speaking for BCS, it further cements that Jimmy/Saul/Gene is destructive and his own worst enemy. He gets a thing going but he juuuuust needs a little bit more. In the face of better judgement and advice, he always swerving the opposite way. Like his brother Chuck said way back when that still haunts him, he doesn't change. He views himself as a victim of circumstances, the world screwing him, etc but its himself that's his undoing. That's why the episode is shot the way it is. You see it play out in the BB timeline and that behavior is manifesting itself again as Gene.
That episode, and the Gene run here to end the series have been extremely well done