Consumer apps are usually designed to do one thing very well; enterprise apps, on the other hand, are loaded with functionality. So, navigation design should be given its due priority. A badly designed navigation system can add time to complete work and of course make the experience frustrating.
Just because there is a lot of functionality exposed to the end-user, does not mean every single option should be made visible as well.
Not all navigation items have the same level of priority, not all are accessed all the time. A great way to reduce navigation complexity is to group multiple items together i.e. create a multi-level hierarchy (two is good, any more than that and you risk making it difficult to navigate and remember). Also, it is very important to work with end-users to validate groupings.
Top Navigation
A great example of this type of navigation design is what you see in the latest version of Microsoft Office.
Sidebar Navigation
Another way to achieve the same is by adding navigation to the sidebar. Adding it to the sidebar takes more space. So, to ensure it does not take space all the time, it is a good idea to provide show/hide option. As for each menu item, you can add expand/collapse option for grouping.
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