This is JMHO. I have developed, thru trial and error, an opinon that unless it gets to be a big build-up of ice we don't defrost. It just seems to me that our freezer works more efficiently with that ice layer. It seems easier to keep the fridge in the safety zone. Now if it builds up and starts blocking air flow to the lower fridge then naturally we would defrost.
When we defrost we leave the fridge closed, turn the unit off and open the freezer door(s). Also, line the empty freezer with about 4 sham wows in the bottom of each side it's back on in an hour and the lower stuff is just fine. I forgot to mention that I have the Oklahoma heat on my side. It's worked well just do it at a time that the sun is not blasting the fridge slide.