Shaving may help
Okay from a restaurant worker's point of view, and someone who worked in a coffee shop for 6 months, please don't just go and use the space if you don't buy anything. Now I will say beforehand that the prospect of you sitting at starbucks and not buying anything isn't going to kill the company.
Anyway if you go to a restaurant of any type and just use their space, be it a booth or table inside, or a chair/table outside that is space that a paying customer can no longer use...and if all the other spaces are being taken up by either paying or non paying customers then the paying customer has no where to go...no where to go now means no coming back later. Now you have possibly lost the restaurant money, and potential customers. It is a proven fact that one disgruntled customer will tell 10 people of their problem with the restaurant...be it sooner or later...then those ten people will each tell 5 people, who will each tell 5 people and so on.
Now I realize this is an extreme situation, but really even if you only buy something for 99 cents please buy something when you use a restaurants space.