My wife and I adopted a Lab two years earlier from a humane society. When she went through puberty, she started acting "off". As in she'd be playing, stop, have no depth in her eyes, and bite you if you got near her. 40 seconds later she was fine and she didn't even know what happened. She even bit the last trainer when she had one of her "seizures." The rest of the time she did every trick and voice command perfectly. After we that, we decided we had to put her down. We spent probably $2000 on training in the year-ish we had her not including the hours calling universities and whatnot for advice.
After many hours of researching, we found out her dad "might have been" a German Shepherd used in dog fighting that had other issues. That dog was shot like a coyote because it kept on tormenting cattle. Would have been nice to know that ahead of time.
We didn't want to go through that again. So we paid the $800, drove 6 hours, saw our new dog get corrected by its father, and be genuinely rambunctious. Now when we go on vacation people argue for the rights to take care of him instead of saying no way.
It's amazing what knowing the family history can do to your stress levels.