It's similiar maintaining your vehicle & your health
It is cheaper to properly maintain a vehicle with regular oil changes, tire rotation, etc. than to ignore the vehicle and then have major problems that cost a lot. It's cheaper to go to your medical provider on a regular basis then only see the medical provider when you are ill. You have a mechanic, a dentist, a doctor...well you also need an attorney that you go to regularly for check-ups!
Talk to an attorney whenever you have a major life event
Talk to an attorney anytime you have a major change in your life - such as marriage, child's birth, death of a relative, starting a business, business problems, etc. The way to remember to talk to an attorney is just do it every 5 years, but sooner if you experience a major life event.