First off, if you already have a power of attorney (Form 2848) filed with the IRS that designated your tax representative to discuss your tax matters with the IRS, this DOES NOT apply to you.
However, as of March 1st of 2013, any new power-of-attorneys for tax matters require separate IRS Form 2848s for each individual. Prior to that couples could complete one form for them both. In other words, one for the joint return. Now each individual will need to complete the form and have it sent into the IRS for the preparer of record to be able to discuss the return with the IRS.
So if you’d like your preparer to be able to handle some of those difficult, long conversations with IRS when you have a tax problem, without you having to go into the office each time and wait while the preparer sits on hold, ask about signing Form 2848. Let your preparer handle those long phone calls. That’s what you pay for after all!