Comment 1 for bug 510077

What I see in Inkscape 0.47:

1) objects duplicated with menu command 'Edit > Duplicate' re-use the gradient definitions of the original (i.e. they share it), unlike copy&paste'd objects.

2) the 'Gradient Tool' allows to assign existing gradient definitions to new objects (i.e. to share it). You can re-use existing gradient definitions from the same list in the fill&stroke dialog as well, once you change the fill from e.g. flat color to gradient.

3) editing a gradient (number and location of stops, color and alpha values) on-canvas results in un-sharing of the gradient definition: the edits only apply to the current object, whereas editing a gradient in the 'Gradient Editor' dialog edits the definition shared by possibly multiple objects and does not assign the edited gradient to an individual object.

4) 'File > Vacuum defs' exists and allows to remove unreferenced (gradient) elements in the <defs> section.

5) 'Inkscape Preferences > Misc > [ ] prevent sharing of gradient definitions' already exists (though reportedly not working as expected - see bug #437926). This preference is *not* enabled by default.