1. When teams are in a tech alliance, it is sometimes the case that two civs may be allied, before they actually meet in-game. In this case, the middle civ acts as a broker, and gifts the tech that they get from the partner on their eastern border to the partner on their western border. This happened in the last game, and enabled Kazakhstan to gift tech to Mad Scientists before they met in game, because they could relay communications through Cavalieros (who had met both teams).
If brokering is turned off, this kind of tech alliance would be more difficult to efficiently develop, because teams that are allied, and wish to share tech will not be able to, simply because their units have not seen each other in game. This will frustrate diplomacy.
Now maybe we WANT diplomacy to be frustrated, maybe we want to stop teams from forming tech alliances. If that is the case, then we need to turn tech trades OFF altogether, instead of turning off brokering.
2. damnrunner mentioned that allowing Normal trading makes tech trading more fun because you have to trust you allies/trading partners not to give your tech to your enemies. This is correct, and it add another layer of excitment and mystery to diplomacy. With No brokering, teams can just trade tech at will, without any worry that the enemy will be given the tech, because no one can trade tech that they have been given, only tech they discover.
In the last game, there was a very painful,
where Saturn made a tech deal with Kazakhstan (The Feudalism Treason) where Kazakhstan gave Saturn tech up front, in exchange for a promise to pay another tech later (after researching it). In an Epic display of dishonesty and shrewd play, Lord Parkin and DMOC decided that Saturn should renege on the deal and not give the tech. One of the excuses Saturn gave for reneging was that they were concerned that their tech would be given away to others... This is an example of the twists and turns and surprises that occur with full trading allowed.
However, if we don't want teams to focus of tech trade
ing, then we should just elimminate tech trades, altogether, because teams can still abuse tech gifts in other ways (ie. I give you rifling you cant trade it to anyone, but you can still gift Rifles to them).