I used to do SWQA. We usually tried to identify the riskiest changes and test them first.
I know how disruptive things can be. One time the company randomly decided to ship an update to an instrument ASAP. The developer had to work nights and weekends for a couple of weeks. Then I had exactly one week to test it. I only had time to test the riskiest stuff. On Friday afternoon, I discovered a crashing bug. The poor developer had to work the weekend so we could ship on Monday.
