Almost any of them increase the risk to others and oneself, and this is the main reason in an always dangerous road where a simple mistake could create a tragedy. It's true that some places establish certain limits to consider it sanctionable but in fact it always is from other viewpoints.
The government acts in the current time not completely banning the consumption, knowing that even a bit of alcohol increases the risk, and it does it also as an opinion that varies between different locations, while genetically the human organism behaves equally under these circumstances.
The following is considering soft beverages and slow quantities:
The reaction time diminishes, and it's technically measured in terms of delay after the stimulus and when the reaction time is vital, a mere fraction of second could be determinant to avoid an accident. From this viewpoint, the use of alcohol shouldn't be ever allowed, right?
The visual system gets more inaccurate so it's more difficult to perceive relative speeds, make calculations and take the appropriate action.
Another critical issue appears when the user experiences the characteristic euphoria and with it there are more possibilities of having ideas that lead to the assumption of more risks like increase speed, make overtakes without the right visibility, take curves without precautions, not respecting the security distance and so on. Especially in the young age, that kind of play costs too many lives.
The movement of the body experiences difficulties so the vehicle movements go clumsier.
Reasons enough for not considering that there are allowed limits and never drink alcohol if the intention is to drive a vehicle. It's an act of irresponsibility that could be strictly fatal, and of course a method of ending between bars, in the worst case having created harm or even death to innocent people, something that psychologically is also another condemn.
Disassociation with vehicles ensures greater security to everyone.