In fact I believe it isn't stating concrete things (ie a lack of formality) that may actually lead to things like Uber.
When you say this is the hours, and this your vacation time, and this is who you talk to about personal issues (aka HR) you are setting an expectation. And yeah you set clear goddamn concrete things like if you get caught harassing or fishing of the company pier we will terminate you. You tell them concretely up front.
When you don't set guidelines people can forget its work and do just plain inappropriate things!