For example, your code might work with version 1.6 of the assembly, but because of the partialassembly reference you might get an earlier version that lacks necessary code.
For example, your code might work with version 1.6 of the assembly, but because of the partialassembly reference you might get a later version that has an incompatible change.
An application that installs a new version of an assembly can break applications that use partialassembly references to load the assembly, if the new version is not compatible.