Very good advice from Rosyna Keller at Unsanity:

When “Optimize System Performance” appears during the update process do not touch your computer and definitely do not launch any applications. Just back away from your computer box as if it were a swarm of bees.

I always do this, and if you’re setting up a new Mac, and instaling lots of apps: One at a time. And reboot between every install. Saves you lots of troubles up the road.