On my last project I tried to use only Share client for configuration but for some tasks had to go back to Alfresco Explorer (v4.0.d). Couple of reasons why you'll need explorer:
1) When you create rule and you apply it to sub-folders, and then you want to override rules on specific sub-folder, it is not possible to disable inherited rules in Share.
2) It is not possible to export folder structure (as ACP) using Share.
One more observation: user groups created through Explorer are visible in Share only when you search for it. When you browse, Share lists only groups created through Share. On the other hand, there are some cool things such as SurfBug.