Honestly? I ignore it, it's a system made up by people who know nothing about maths, the only time I ever see this system being openly used is on those Bitcoin faucets and so on and I think it's just a way to disguise how much they're giving you. There's nothing difficult about writing or understanding 0.00005 BTC, this is coming from someone who scored an F in Maths.
Actually the metric system was designed by people who do know about math.
It's a convention that reduces the amount of 0's you have to write or type (before or after the decimal).
But you don't want to switch. For example, in physics you typically use mks - meter, kilogram, second where in chemistry you typically use cgs - centimeter, gram, second
And you don't switch between them in your paper.
Once you paper uses mks you don't then give values in centimeter because your paper already uses meter.
With bitcoin, exchanges should always use a BTC (just like they always use a dollar)
For other applications, use the unit that results in the least number of needed repeated 0's thus reducing typos.
For me listing stuff for sale that's probably mBTC
