I've seen a lot of startups which missed to think about founder vesting in the beginning. One year later the "co-founder" holding 50% decided to travel around the world because "this is way to stressful...". This can cause some serious trouble talking to potential investors.
You are also right! I think if you've build several products before it's more easy to choose the right path building great products. But I do also see a lot of people just building something behind closed doors without thinking about the problem they really want to solve. Of course, justyo.co for example... I don't think there was a huge need in sending YO's :D