Is Merging Classes With Proguard Recommended On Android/dalvik?

It just occurred to me that one of the ProGuard code optimizations we used, namely merging class hierarchies, may perhaps not be a good choice at all. My hunch was that it would be

Solution 1:

Vertical class merging collapses classes/interfaces with their extensions/implementations when these are needlessly split. That should always be an improvement (size and performance).

For horizontal class merging, I can't provide a general answer. The code base will be smaller, but some code could conceivably be loaded to soon, or in the extreme, unnecessarily.