What is the correct measurement systems for animation? In animation, which scale or measure system should I use? For example, If I model an entire room and plan on having a character moving about in it, should all the assets and character be done to real world values or should I use Blender units?

I'm asking this because sometimes when I make a character and scale it down to it's "real size", I sometimes have issues with simulations or hair particles because of the character being to small in the scene. Like having to use very small values to tweak values(example:o.oo5 in particle hair uniform slider instead of 0.5), which sometimes can make tweaking very finicky.

So I wanted to know which is way that is most commonly used.
The best way is using the reference unit. for each animation you should have a proper reference footage or etc.

For example you want to create walk cycle. you start to walk in your room and observe Walking variables by taking a footage from it. when you want to use that footage, you should use a measurement system With which you understand your footage. for this example metric unit maybe is the best choice.

But when you want to simulate a animation in big scale, you pick a proper ratio of a small unit that can describe the actual scale. for example the space between moon and earth is 363,104 kilometers. you can use metric unit and set it 3.63 meter to get the best result.