I might normally say that you should trust your players, especially when I'm a player, because as a player I want group cohesion and I trust myself to give equivalent rewards.
But as a Designer, and less so as a DM, all it takes is looking at a freeform RP board for that ideal to crash and burn faster than Icarus. When designing my game, after being well familiar with the horror stories of 3.pf
and Ars Magica (its magic system is both a blessing and a curse), I instantly latched onto bounded accuracy and having well-defined nuts and bolts. I really like the idea of freeform magic, and I'm not super big into needing rules for rp, so I settled on having a system where people can break down the effects of a spell into small chunks and rearrange them as they see fit. Players can combine any number of effects or modifications as long as the total cost stays within your Magic stat's allotment, and the spell effects exist in the first place. I've expanded that idea into a lot of other mechanics in the game, including weapons, armor, actions in combat, character growth, and more. In my mind, its like a kitchen. You can make whatever you want as long as you use the ingredients in this cupboard. There's still a lot of room for creative expression, but both the designer and GM will know what ingredients are in that cupboard.
As far as rewards, I trust the GM with running the game as they see fit. I put more trust into the GM as I would the players, but I also figure I'll want to add in a bunch of tables so that it might be possible to run without a GM. In that case, Players would get full trust, as they are all now part GM and will run the game as well as they deserve. I try to write my rules to guide participants towards the intended playstyle, but I also know I can't really stop anyone from doing anything once its out of my hands.