fourth suit round or gameforcing?

[foo]

Here's the fundamental trade-off:

 

If you use 4SF for Inv+ hands when you have enough room, your game bidding will be more accurate but slam bidding will suffer.

 

The opposite is true if all 4SF bids as GF. You get to use the sequences less, but when you do it conserves space for slam exploration.

 

An example of the potentially bad sequences are

1H-1S;2C-2D! vs 1H-1S;2C-2N

 

If the 1st is GF, then an Inv responder must use the 2nd whether they have 4??? or 5???. Which means when opener passes with a minimum We may play 2N with a 3:5 ♠ fit.

 

OTOH, if the 1st sequences is Inv+, We will more often get to our ♠ fit, and more ofen bid games based on that fit, but opener must jump rebid 3N with extras (...and what does opener do with a Max w/o support or stops in the 4th suit for NT?). This potentially cramps slam exploration auctions.

 

Particularly playing MPs instead of IMPs, better game bidding at the expense of slam bidding is worth it because MPs is a frequency game rather than a expected pay-off game.

 

(exploration of the implications of the other sequences left as an exercise for the reader. :) )