If operating in visual conditions, and can maintain your own terrain separation, you do not need to adhere to the departure proceedure, unless cleared for a specific departure proceedure.
Minimum climb gradients are applied to gaurantee terrain separation (obstacle clearance) for the departure route specifid in the DP. Without maintaining those climb gradients at a minimum, one cannot be assured obstacle protection.
Operations manuals and opspecs may require an operator to adhere to the departure proceedure, but under Part 91, an operator is not required to do so. All operators are strongly encouraged to file, and to fly, departure proceedures.
If not assigned a departure proceedure, a pilot may determine the proper departure. If guidance is provided in a DP, the pilot may fly it, and should fly it unless able to assure obstacle clearance. AIM 5-2-6(d) advises that each pilot should "determine if obstacle avoidance can be maintained visually or if the DP should be flown, and...consider the effect of degraded climb performance and the actions to take in the event of an engine loss during the departure."
Departing ASE, I always fly the proceedure, regardless of weather conditions.