The fact that ThinkIQ is a type-based system means that you can leverage pre-defined types when creating your model, and your model will be consistent and rule-based. It also means you could export your model, for example, and use it to start a new model for another site. There are a lot of reasons to build your model on consistent types.
Sometimes, however, you may find that you need to tweak just one attribute on an instance, or add an attribute that applies to only a few instances of a type, while all other instances of the type remain the same. For these exceptions, you can create a maverick attribute.
For example, you may have just replaced a pump and the new pump has a pressure sensor on it that your other pumps do not have. You want to wire the sensor and start collecting data on that pump's pressure. Do you need to create a new pump type that includes this attribute? You could do that - you could create a specialization of pump that includes pressure, but if you only need to use it in one place in your model, you may not want to bother with that. In this case, you could add the attribute 'pump_pressure' to the instance of the pump, wire it to the sensor tag and start storing data. This is what a maverick attribute is good for.
Maverick attributes are like all other attributes and can be treated as such. It's data source can be wired to a tag, could be internal, an expression; it's data type can be any of the standard types (float, Boolean, string..); it can have a range and limits. It is a full citizen in the world of attributes. You will know if you are seeing a maverick attribute when you look at the attribute list of an instance. Inherited attributes - those inherited from it's type - are lightly shaded. Maverick attributes are plain white.
Mavericks should be used judiciously. It may be easy to simply adjust an instance here and there, adding different attributes, but the negative is that you have now created an exception. This instance is no longer the same as other instances of the same type. Scripts may not behave the same way - or perhaps you need a new script just for this instance. You may need to remember that specific instances stand out or behave differently. Once you exploit mavericks, you begin losing the benefits of a strongly typed system.