tran oil change or pwr flush

Not knowing the past of my '88 R10 suburban except that both the original owner and I use it to tow our trailers I figured I would get the transmission filter changed. A major transmission chain near me usually offers a good deal on a filter change, band adjustment and change whatever fluid drops out. I know that they will insist that I MUST HAVE the power flush option. Is this really necessary?

Thanks in advance,
Jon