What is the result if the daughter volume is larger than mother volume?

If the daughter volume is not totally inside the mother volume, what results do this cause to?

This causes an overlapping volume, some of the consequences are discussed here, and more generally in these posts.

Since, there is overlapping, why the application can successfully run?

because geant4 does not check for this kind of errors. the run seems successfull, but the results are (most likely) not correct.

the user is responsible to provide correct geometry to the software.

Overlaps checking has a performance cost, so it is not done by default (as @weller said, it’s the user’s responsibility to provide a valid geometry). You can ask G4 to do overlaps checking by passing pSurfChk=true as the last argument (after the copy number) to G4PVPlacement.

In our simulation framework, we have a data member for our geometry vitural base class, with an associated “checkGeom” UI command, so this can be turned on or off for the whole geometry.