What Acolyte said, with the added note that Spirits have Edge equal to F/2 (a fair rebalance from the overkill F in SR4). That rule, by the way, was in Street Magic as well, together with the rule that Spirits can (and under specific circumstances will) use Edge to resist Summoning. So these rules are clearly not meant to contradict each other.
The idea is that Summoners would argue that a specific roll was part of what the Spirit MUST succeed in, so the Spirit was supposed to use its Edge. Against that a rule was made clear that this was indeed not intended and would not happen. If I recall correctly, SR4 did not have the option SR5 introduces, namely that the Summoner uses their own Edge for such crucial rolls.) So it was meant against abusing a Spirit's Edge Pool by the Summoner, and still is. RAI of this rule thus is completely unrelated to using the Edge againt Summoning