AB on Gibraltar would give the allies a major boost once more. The US/UK would be able to bring fleet over and stack the Gib sz a turn sooner then normal w/o worrying about a strike from the Luftwaffe because of the scramble. Even if the Italians open up a landing spot for the Luftwaffe to land in N Africa, the Germans probably aren’t going to risk it with 3 more ftrs sitting on the AB in Gib. I will say as the allies I miss it though.
As the others have said an AB on N Italy would put a stop to Taranto. Probably not good for the game, and I don’t like to make changes that will effect the first round of play (that’s why I’m not a fan of bids that allow immediate placement in key areas at set-up). Maybe Sicily would be a better place for an Italian AB and historically correct as well. Sicily was an important air base to the axis, was used to harass allied shipping in the Med, and offered protection for the Italian ships as well. It wouldn’t have an effect on the opening moves either.
In game terms the pro for the axis is they could use it to def sz 95 with up to 6 air units when the US comes a calling. I don’t think it would stop the allies, but could delay them for a turn if the axis put 3 frts on Sicily. Sicily could become a target for the US as well (lets face it Sicily is irrelevant in G40). I think you might have to add a an inf or two there at set-up?
In the long term though the con for the axis is an AB on Sicily might help the USA. Say the axis have 6 air units that could scramble (3 S Italy, 3 Sicily). This delays the US attack on the Italian fleet, but eventually they manage to force the axis air out (or kill it), destroy whats left of the Italian fleet, and Invade Sicily the same turn. Then good ole UK drops 3 ftrs on Sicily to protect the Damaged US fleet in sz 95, which hurts the Luftwaffe counter attack (maybe not so good for axis lol).