Posted 2023-January-18, 06:48
Opener is supposed to make a decisive call immediately. The invitational jump shift shows a hand too weak to force to game but too strong to bid via 1NT. When used by humans it shows a concentration of values in a long (6+) minor suit that will serve as a source of tricks, usually in 3NT, approximately 9-11 points and denies support for opener's major (3-card support is right out, some people also exclude Hx). With a non-minimum opener will usually bid 3NT or jump to 4M (with a long strong suit of their own), especially with some support for the minor. You no longer investigate stoppers. A bid in a new major offers responder the opportunity to pick the least bad major game, but you'll often be playing in a 7-card fit. With more than a minimum blasting 3NT is the percentage action. Responder likely has at least one of the two unbid suits stopped, or two half-stoppers combine to make a full one, or the opponents will fail to find the killing lead.
The key insight is that while you might not know whether 3NT is best, partner certainly doesn't know. You could have practically anything on the auction while their hand is narrowly specified. Asking them to weigh in on game choices is mostly a form of torture.
Theoretically other bids should be used for slam tries, but this is up to partnership preference.
I have no idea how much of this, if anything at all, works when playing with GIB.