Well, after you cast something through it, or it goes out of sight, it returns to you and hovers.
As a DM, this means it will be inside the sphere with you. And you've expended three spells to cast one (of 4th level or lower) successfully. Okay, you're out of the fight unless someone with teleportation, dispel magic, disintigrate, or other things that will eliminate/bypass a resilient sphere. As it's kinda hard to get three spells off in one round (although possible, with Quicken Spell, a familiar and a Ring of Spell Storing; other methods exist) this will normally mean your opponent has a chance to do something mean to you before you cast back.
Of course, about the minimum you could pull off the three spells in one round is 9th... and then what you're hitting someone with is a 1st level spell. Unless you run across a Lesser Metamagic Rod of Quicken (use it on the Spectral Hand) to go with. You're looking at about 85k in equipment to pull this off in one round before 9th+. And you shouldn't have 85k of equipment until sometime between 11th and 12th. When you could Quicken the Spectral Hand on your own (and would still need the Ring of Spell Storing to get the third spell off, for 50k).