Recently I was asked to quickly summarize why EightShapes usually chooses Adobe InDesign as our baseline tool for creating user experience documentation (in particularly, sophisticated systems for wireframes and annotated deliverables). I should have a set series of slides on the topic. But I don’t.

Admittedly, InDesign’s learning curve for getting started exceeds most if not all other popular design tools. But with that investment to learn the tool comes a power to modularly create and collaborate on design solutions and documentation.

Usually, the choice of InDesign over Visio (or Fireworks or Illustrator or Omnigraffle) for a wireframing system boils down to points like:

• InDesign is cross platform (Windows & Mac). If you want everyone to play, including vendors with unpredictable platforms and/or a nagging disdain for Windows, then Visio AND Omnigraffle are quickly dismissed.
• InDesign is by far the most modular, with snippets, object libraries, and capabilities to dynamically link files to one another. Visio is on the other end of the scale, with but the use of stencils in narrow ways to control instances within a single document. Visio documents are where screen visualizations (in this case, wireframes) are embedded with no opportunity to reuse within (such as a wireflow) or across (such as multiple deliverables per project) documents.
• InDesign’s  style power (rather, distinct style types for paragraphs, characters, objects, tables, table cells) includes such a deep array of customization, inheritance, and typographic control that vastly exceeds any other tool for creating wireframes and managing a system based on a formed, mature visual system. Sure, it’s wireframes, and they aren’t meant to be pixel perfect. However, systematic wireframes should reflect the established visual conventions of structure and behavior that typography and basic object styles can imply.
• InDesign is for creating annotated documents. While both Visio and Omnigraffle also support a page model for publication, Illustrator and Fireworks are solely dedicated to creating screen visualizations, not associated annotations that can be detailed, versioned, and so on. Additionally, InDesign’s embedded features for document variables, rapid TOC creation, and application of standard layouts enables designers to more rapidly produce more polished documents.
• InDesign supports more powerful grids, vector-based drawing tools, and layer organization than non-Adobe Creative Suite products, with a similar goal to that of typography: implying the standard visual conventions for laying out different page chunks.
• InDesign empowers collaboration across resources not limited to UI/Information Architects/Interaction Designers, but also content strategists (via threading InCopy with InDesign), visual designers (with InDesign’s fully featured placement and control of Photoshop layers and layer comps), and others. InDesign is a publishing platform built on collaboration. Visio and Omnigraffle are made for a single person to own and publish a document in isolation.

The big theme is that InDesign provides the only software tool on the market today by which you can unify delivery of user experience documentation across a range of disciplines. The result? Increased collaboration between designers, governance across designers, and credibility of the design organization outwardly to other groups. Otherwise, it’s every designer for themselves.