There is a bit of controversy about that. On older trucks that haven't had the transmission serviced, there is some risk in dislodging particles, and causing collateral damage, so to say. Pressure flush at a dealer or independent shop is more likely to cause that.
Personally, and since I do regular, periodic maintenance, I prefer to do a more complete exchange than just a pan drain and fill, since the drain/fill only gets something like 40% of the fluid changed.
The service manual seems split on that, however. Standard procedure is drive until the tranmsision is hot (80 deg C, 176 deg F), drain, measuring the amount removed, and refilling with the exact amount measured. Drive, recheck, and "if the fluid is still dirty, repeat" [drain and fill]. Don't reuse the transmission pan drain plug gasket, replace it.... so best to have a couple on hand.
Alternatively, the service manual also adds (quoting directly, now):
• To flush out the old A/T fluid from the transmission oil coolers, pour new A/T fluid into the A/T fluid charging
pipe with the engine idling and at the same time drain the old A/T fluid from the auxiliary transmission
oil cooler hose return line.
• When the color of the A/T fluid coming out of the auxiliary transmission oil cooler hose return line is
about the same as the color of the new A/T fluid, flushing out the old A/T fluid is complete. The amount
of new A/T fluid used for flushing should be 30% to 50% increase of the specified capacity.
Search on transmission fluid changes and you will find some recent threads where folks have shared more how-to tips on that procedure. That will exchange essentially all of the fluid.
My thoughts - if your transmission fluid looks and smells like fresh ATF, and if you are going to refill with NissanMatic S or J, then you would be fine doing the simpler drain/fill. On the other hand, if you are changing to a synthetic like Amsoil, Red Line, or other, then I prefer the more complete exchange, although even then, it's not required, as the fluids should be fully compatible.
Long winded, but hope that helps.