Nucs... Always have alot to say about them.. Ted hit most of it well.. having nucs for spare parts as stated is the bees knees. You don't have to pull resources from a production hive if you have nucs available...
if you lose a queen, or have a queen failing you can snag a queen out of a nuc, put her into a queen cage and introduce her to the hive that was going south and let the nuc raise a new queen... you dont lose production that way.
Keeping nucs to replace losses in the spring. A hive lost to mother nature and old man winter replaced with a nuc will most likely produce honey that year if you reuse the drawn frames.
You can combine a nuc to a queenless hive / newspaper method and end up with a good strong hive with a real chance to produce honey...
You can pull larvae / graft from a nuc instead of a production hive.
Let a strong nuc raise queen cells to replace aging queens in your production hives.
Putting a damaged frame in a nuc usually yields fixed frames of worker cells instead of drone cells.
You can raise new queens in nucs to sell, or sell the nuc..
I could go on for a while.. there is limitless possibilities if you have a few nucs ready...
5 frame nucs used as production hives? I know three people that do it. They are retired, and get into those hives about every week in spring to keep them managed. They are constantly splitting when they get too strong, and selling the extra nucs with people always wanting more than they have.
One thing to consider if deciding to go with 5 frame boxes.. those guys and one gal put ratchet straps around them when they get over four boxes high (Mediums) They also put them side by side, one hive facing one way, the next hive facing the other way, to keep them from getting blown over in a storm. With the straps binding them together they hold up well if they do get knocked over, but the bees are usually a little miffed when you stand them back up.
I think when I reach the age I start to have difficulty I will go to 8 frame medium boxes....
I do have to say, my observation hive in my front window does really well being three frames deep and seven boxes high. I do have to split them twice to three times each year to keep them from swarming.
Scott