It is about aligning risk preferences. Being "all-in" is not likely a good thing for a founder. The founder prefers to take less risk which results to mediocre exit for the investor. The investor would rather have bigger exit or nothing, and giving the founder some money is helping to aling the risk preferences a bit towards the same direction.

As for employees? They are typically not calling the shots about company direction. I don't see a reason why investors would care about employees.