Hey CG friends !
I have modeled a Robot in Blender, and the beast is actually composed of various objects. I have no idea whether I should first join all the parts, apply the symmetry in the process and the rig the character, or if I should leave symmetry on, or if I should rig each part separately.
I plan to export it to Unity and I would really love some advices (: I’m actually more used to model human character, so they usually do not have free parts. 
Thanks a lot !
You can leave the parts separate… what I usually do is join everything together into one object, applying all mirrors, rig the character and parent to armature with empty groups – that will put all the necessary vertex groups into the model. Then you can separate the parts out again. Then I mirror each part, do the weight painting to one side, then apply the mirror again. Blender will automatically apply the proper weights to the mirrored side, due to all the necessary vertex groups being present when you parented the model to the armature.