[Context and Motivation] It is common for teams to take shortcuts during software development that, in the future, will lead to maintainability issues and affect productivity and development cost. Different types of technical debt may affect software projects, including those associated with software documentation. Although there are many studies on technical debt, few focus on documentation debt in an industrial environment. [Question/Problem] We aimed to identify how software practitioners perceive the occurrence of documentation debt in their projects. We present a combined analysis of the results from two complementary studies: a survey (InsighTD) and an interview-based case study. [Principal Ideas/Results] We provide a list of causes and effects of documentation debt, along with practices that can be used to deal with it during software development projects. [Contribution] We find that documentation debt is strongly related to requirements issues. Moreover, we propose a theoretical framework, which provides a comprehensive depiction of the documentation debt phenomenon.