Most are well aware of the major and obvious advantages it can provide: tandem gym attacking, staggering gym attacks, berry flooding, trading pidgey for ralts, friend attack bonus, extra raid balls, shiny chance is doubled, almost double the exclusive CD move opportunity, etc to name several but not nearly all.
Smaller advantages would be to
1. battle a very boring gym with one hand and catch everything around the gym with the other hand. Pre-fight animation is so long that with the other you can catch and check appraisal on what is around.
2. The extra one can spin a pokestop and check the field task and you can decide whether to proceed with the other’s current tasks or switch.
Any other less thought about advantages? I would hope/anticipate 90% of extras would be totally free playing, but might Niantic get a payment for every Starbucks or Sprint postcard/gift sent?
Well-reported in December they were getting quite a big chunk of change for every sponsored pokestop spin. I imagine this gifting is a more tangible promotional commodity, even if the same person gives and receives that gift.
Then maybe with the chain raiding of Articuno and Zapdos people are actually roped into buying passes for both phones looking for the limited time shiny offer.
Also from what I’ve heard Sprint/Boost/T-Mobile whomever sponsor can wring out real money for some phone plans to have tethering access, that could be a monetary influence
Any other suggestions why a ghost/free account actually could be worth sponsors/Niantic purposely/blindly allowing?