Both eyes epiretinal membranes & cataracts. dr said i have option of vitrectomy and cataract removal in both eyes on same day. is this a good idea?

Not necessarily: I'm not sure if your question is phrased correctly. In the US, only one eye is typically operated on at a time for elective intraocular (internal) surgery. If your doctor is suggesting removing the cataract and repairing the membrane in a single eye during one surgery, that is a different story, and is not without debate. Removing the cataract alone may give you acceptable vision.

ERM & Cataracts: Epiretinal membranes (ERM) can affect central vision. Often they do not. If OCT (optical coherence tomography) shows a significant ERM, removal at time of cataract surgery is recommended. If ERM mild, it is ok to remove cataract first: but know pt may need ERM removed in future.