I think this would need to be examined on a case by case basis, and sometimes there is a purpose to the hybrid tags.
I think hybrid tags need to be evaluated on a case by case basis.
- Do they identify a field of expertise or interest that is not of fully of interest to one or more of the component parts?
- Do they identify a unique field of interest or expertise?
First lets try an abstract example...
Lets think about motor, bicycle and the potentially hybrid tag motorcycle.
I would argue that the latter is more than just the sum of motors+bicycles.
The resulting field is more than the sum of it's parts. Sure somebody could find questions related to motorcycles by combining the tag, but to do so you abuse the scope of the more specific tags. The area of expertise for motorcycles is not just make up of folks that know about engines and folks that know about bicycles. In fact being an expert in one or the other of those other tags probably specifically mean you are not interested in questions about motorcycles unless there was a specific aspect of the question that was a cross over issue.
To the motorcycle expert looking for questions he could easily find the right ones if he knew that a combo was what was required. However for the mountain biker enthusiast having motorcycle questions in their bicycle feed would be unwanted noise, as would having questions about disk brakes in the motor feed for the diesel engine mechanic. Only having the hybrid tag motorcycle keeps the respective areas of expertise/interest duly separate.
In this example, having a motorcycle tag would preclude the use of motor or bicycle on all questions about motorcycles except as they were specifically related: a question about how motorcycle engines work might have motor and a question about whether rules of the road are the same for cycles as motorcycles might have bicycle.
Back to your specific example...
I think your specific case study is an analogous to my fictions example.
Knowing a little bit about Android and its SD Card system, this is almost a different beast than standard SD Card issues. Experts in SD Card issues across multiple platforms would be baffled by the kinds of issues raised by android users because they are operating on a layer of abstraction not normally present. In this case I think it makes sense to specifically identify them as their own subset, not just by the union of two other tags.
The tag android might be used in combination with android-sdcard but using sdcard for questions that were about Android's sdcard access api would not be appropriate as that is really a separate unrelated area of interest.
There are some hybrid tags are not backwards compatible with the composite parts. They are a field of their own that is more than the sum of their parts. They are likely not of interest to one or more sets of experts that cover the à la carte tags.