Answer to Question 1
Vagueness occurs when the parties do not want the contract to be clear. They want to keep their options open, so they don't clearly define some terms.
Ambiguity is different --- it means that the provision is accidentally unclear. It occurs in contracts when the parties think only about what they want a provision to mean, without considering the literal meaning or the other side's perspective. Any ambiguity is interpreted against the drafter of the contract.
Answer to Question 2
Businesspeople are optimists - they believe they have negotiated a great deal and everything is going to go well - sales will boom, the company will prosper. Lawyers have a different perspective - their primary goal is to protect their clients by avoiding litigation, now and in the future. For this reason, lawyers are trained to be pessimists - they try to foresee and protect against everything that can possibly go wrong. Businesspeople sometimes view this lawyering as a waste of time and a potential deal-killer.