Almost everyone seems to be using ERC20, but not everyone is. I wasn't able to find a comprehensible overview of subcurrencies standards/usecases and pros & cons of using ERC20 in your system / resources that compare tokens implemented for different systems.
As far as I understood it is possible to have different divisibility and even affect gas costs for your contract or a system of contracts depending on your subcurrency parameters.
My impression was that the popularity of ERC20 by large explained by adoption - that it makes it easier for 3rd parties to integrate it in the outside of Ethereum contexts.
Can anyone recommend a good read explaining other reasons for ERC20 popularity that helps to wrap one's head around whether it makes sense to use it, spend time and effort on your own implementation or look for other implementations that have been tested to a certain extent.