The first one refers to how g-force is a measure of a relative acceleration experienced in terms of 9.8 m/(s^2), which we know as g. This is irrespective of the mass of the object and hence it relates to the relative acceleration of an object and can indeed be applied universally. By mentioning forces, the mass of the object matters. 10000 N might not seem like a huge amount of force for a 5 tonne truck but for a human being, experiencing this amount of force to the body could be fatal.
As an example, by measuring this in relative terms to g-force, a relative number can be deduced allowing someone to calculate the required force to act on an object to apply a certain amount of damage or deforming etc. So if that 5 tonne truck experienced a massive deformation at 5 g's to the front, then 245 kN of force would have to be applied to cause that much damage and deformation. Or if, for example a person had to experience a 5 g shock to the whole body to end up in a coma, then saying the person was 70 kg, approximately 3430 N of force would have to be applied to the whole body.
Yeah in terms of psychological effects, basically the environment a person is under can be investigated through the use of g-force. For example, weightlessness can be observed to occur at a certain time and for that to happen the acceleration of the body relative to Earth is zero. This can have different effects on the human. So it can be used as a tool to examine the load that the astronaut is experiencing relative to g.
