I mean, I guess you can use the second one to shoot if the second shot isn't an attack. But what the hell else would you do with a shot?

Do not ask Me !
I did not invent the SR5 Rules
I'm merely stating them
(and pointing out that the SR4A Rules made more sense to me

)
@Medicineman, why do you think it's so OP two attacks per Combat Phase?
SR5 Weapons do sig nificantly more Damage than SR4A Weapons ( 150 % mostly)
and If your Char (or the NPCs ) have (f.E.) 3 Inipasses, this would mean, they cann Attack you 6 times , twice as often as by RAW
Even though Armor also raised by about 150 % and You can dodge now with REA & INT (instead of only REA in SR4A) the Damage output of the Guns is more extreme than the protecting Factors of Dodging and Armor.
Imagine an Enemy with an Enfield AS 7 Assault Shotgun in Burst Mode firing Twice at You with 15P ( AP +4 for Shot rounds) and ....3 Successes each . And Your char getting -1 to Dodge because of the Choke....
and in the second Inipass he attacks maybe only once because of Recoil, but twice again in the 3rd pass.
That would be 5 Attacks in 3 Seconds....
But this is just an....educated Guess from me . You should try it at your own Table
Your own experience is far better than a calculation that I made

with an educated Dance
Medicineman