Probably the first reaction for everyone would be: Hell no!
I believe though, that the right answer is: yes!
Most people forget the agile is not about planning – yes, in most cases we take Kanban, Scrum, TDD, and etc. for managing and planning the development process but all those activities are not actually part of the initial agile description – Manifesto for Agile Software Development
Furthermore, ad hoc is word used often with negative outtake, it gives us sense of chaos and unpredictability, which is not considered as good even in small dynamic companies. I believe, that ad hoc could work in a way. If company development resources corresponding with the task requests coming daily, the planning is not really necessary even quite the contrary it could be waste of time.
I believe, that planning doesn’t necessarily means increased productivity and better process handling by default. For agile, the people are the greatest resource. I believe that experienced enough developer could be better in planning on the fly and making educated guesses about the severity and the importance of tasks than most managers.