As far as I can see leasing has only one good point. When you are building your business plan, and cannot figure out how to amortize costs for items that you might have to purchase, just plug the lease cost into your per-month figures. You'll be able to see how much money that vehicle or machine will cost in immediate comparison to how much money it's making you. Also, because the lease cost is higher than an amortized purchase, you'll be less likely to get caught up by the errors of your unfounded dreams.
It is occasionally proper to lease a vehicle for a particular contract that you need to accomplish. For example, you have just bid on a contract to put in a sewer system, and at the end of the job you will no longer need the Big Sewage Truck, so if you get the contract, you lease the truck. The lease cost is built into your bid, so you won't accidentally win the bid by underestimating your cost, and when the job is done you won't have the problem of "What do we do with this useless truck?"