Some of Google's iOS apps, as well as other apps (e.g. StackExchange for iOS) use a combined navigation model based on both a Tab Bar and a Navigation Drawer (aka Hamburger Menu). Typically, the Tab Bar will offer navigation to the major sections of the app while less-frequently accessed destinations (such as Help and Settings for instance) will be accessible from the navigation drawer.
What are your thoughts about this approach? Is it a good practice or a strange hybrid?
Like with most questions like this, the tl;dr is: It depends.
The correct navigational pattern is largely contingent upon three things:
App structure
If your app is structured such that you can support fewer than 5 first-tier leaf pages, a tabbed approach is great. If there are additional pages that aren't contained in a core user flow, it can make sense to include additional functionality in the ☰ menu. These include:
Leaf page functionality
If leaf pages are sufficiently differentiated from one another but equal in hierarchy and priority, tabs is a pretty solid mechanism for navigation. Examples of this include:
Desire to enforce prioritization by the product team
This is less about the discipline of design and more about its practice. Product teams have ever-evolving requirements, and as a result, the product/service can become bloated and unfocused. Choosing a fixed number of core user tasks and placing them in tabs helps design teams push back against product creating a junk drawer filled with long-tail functionality and enables the team as a whole to spend more design and development time on core functionality.
Further considerations
Try to avoid user tabs as a sorting or filtering mechanism. In your G+ example:
there are states in which users have top and bottom tabs, and the top tabs serve as filters for content in "Collections." The content within the "Featured," "Following," and "Yours," tabs is the homogenous. This is a strong anti-pattern for tabs. There are much better filtering mechanisms.
Additional resources
An update on the Hamburger Menu - evolution of the usage of the hamburger menu
Who Designed the Hamburger Icon - history of the icon
Why and How to Avoid Hamburger Menus - practical guide
I hope that helps!
You have already highlighted the core functionality of tab navigation and off canvas menu. The only drawback I could think of with such design is the screen estate available for the actual content. However mobile phones are getting bigger so I don't think this would be an issue in the future.
Whether to implement off-canvas or tab navigation or both depends largely on the site architecture and also the goals you want to achieve. If your goal is to drive more users to a particular page(s) or perform certain action(s), you may want to put the links in places where user can easily access. Since tab bar can be navigated and clicked with one hand, naturally you would want to put your links there.
