My $ 1 million personal lines umbrella policy requires that I have $ 300,000 liability on my auto and homeowners insurance, and $ 500,000 liability on my motorcycle insurance. So, I have $ 300,000 liability limits on auto and home and $ 500,000 liability limits on my motorcycle. Plus up to $ 1 million excess coverage through the umbrella policy.
I carry these sort of limits because I am a middle-aged professional with lots of assets (cash in the bank, retirement accounts, real and personal property, and future earnings) that could be seized to satisfy a liability judgement. The fact that I do liability for a living colors my opinion on these matters.