Actually it does have an advantage for the player. I am guessing that the player that wishes to use the construction or research cheat is concerned about helping the AI out at the same time. Although you will help them somewhat, it will not be as drastic as say what help you will give your own country. The AI is not going to turn off all the officers, Diplo points and Espionage points so they will have less research started. Also the AI will probably pay more attention to the research years than the player does. So if you want to increase your research and do so by more than the AI just apply all the leadership into research and choose the techs that you want. Carry them out to what ever year you want and viola you have an advantage over the AI.
Same goes for construction. the AI is not going to turn all IC to production. So the player would produce more units during the cheat than the AI.
The cheats are not as efficient as you might like, but I am betting it will still give you a significant advantage.