It's my first post here so take it easy if I am silly.

My decision was 18/17 and 8/4, however gnubg recommends 18/17 and 6/2, saying my move is -0.115 compared to the optimal one.

I really don't understand why it is better to risk my opp rolling a 2 and taking control of the game, and 8/4 is a great setup for more points on the 2 or 1 point.

Black can't "take control" while you still have your prime. 8/4 is actually the riskier move.

6/2 is a standard play when you have a 6-prime. Even if Black hits you, he still can't get out. Playing 8/4 actually gives Black a 6-2 shot to get back into the game.

Thanks a lot guys, made it a lot clearer now.

How about this 3-1 recommendations to take 8/4 instead of 24/23 8/5 ?!

The blot on 8 is a big target anyway, with any 6 or 4 reaching it. 3-1 is about as bad a roll as you could have gotten here, so you won't be able to leave yourself developed and safe. 24/23 doesn't do anything, nor does 8/5. You might as well try to make something good happen with the 8, since bringing down extra builders leaves them in the line of fire also. 8/4* impedes the formation of an advanced anchor, and if you are not hit back, I think trading your 7 for your 4 point is ok, if it comes to that.

8/4* is vital in this position, in fact any other choice is a blunder. You want to prevent your opponent from anchoring on the 4 point, so you must hit him off that point. If you leave him there and he anchors on the 4 point, your advantage is gone and his equity is a touch under 50%.

If he rolls one of the 9 fanning numbers you have a strong double and even though it is a take, there are many players who would drop here.

In addition to the 9 fanning numbers, 6/1, 6/2, 5/1 and 5/2 from the bar are nightmare numbers for him to play.

Finally, even all of his good numbers, with the exception of 4/3 from the bar only make him a small favorite. 4/3 is the one joker from the bar that makes him a decent favorite.

About 50% of my big errors involve hit or no hit. Trice has good rules of thumb. Also
"What are u going to do productively next roll if you play your roll vs the aggressive looking hit" is a thought process that can sometimes lead to the correct decision. Not so much here tho.