That's a matter of choice. Not really necessary, but there are advantages (and disadvantages):
Good:
1) Will ensure a fresh spare forever ("shouldn't" make much difference until decades later.
2) Prolongs the time period slightly (25% more) between new tire purchase requirements.
3) Removes limits on driving with spare (speed etc.) if you need to actually put it on the truck & use it
Bad:
1) Takes up more space in the trunk. (not a big deal)
2) Costs more (likely 25% more) to replace a 'set' of tires.
3) Requires more time/effort to rotate tires.
4) Requires an additional TPMS sensor to be bought/maintained.
5) Complicates the "winter tires" equation for those with more than one set.
6) You may actually over-extend the life of a 'set' of tires beyond point where "age-wear" is more critical than "miles-wear". This is for those that put very few miles per year on the vehicle.
7) You CANNOT use rotation-direction-specific tread types, without losing the benefit of having the 5th tire (it can only be used on one side, so even rotation among all 4 tires is impossible).
Personally, I can't really think of a 'justifiable' reason to do it, unless you've got specific road/region related peculiarities that don't allow the smaller spare; but otherwise it's a personal thing. Back in the bad old days, it made sense, due to more critical wear factors for tires. They just didn't last as long for various reasons, and moving the tires around could help even out otherwise uneven wear, just generally prolong the life of a set. That problem, which used to be fairly commonplace, has been pretty much eradicated by technology (improved tire, wheel, vehicle, & balance/alignment equipment) over the decades. If your vehicle & tires are properly maintained, you should be fine just rotating front to back.