What is the logic behind having so many decimal places for cryptocurrencies like btc and ethereum
How is it decided for a new crypto, does it depend on coin supply
This one's pretty easy to answer, just read this answer by Cryddit
I remember this discussion, actually.
Finney, Satoshi, and I discussed how divisible a Bitcoin ought to be. Satoshi had already more or less decided on a 50-coin per block payout with halving every so often to add up to a 21M coin supply. Finney made the point that people should never need any currency division smaller than a US penny, and then somebody (I forget who) consulted some oracle somewhere like maybe Wikipedia and figured out what the entire world's M1 money supply at that time was.
We debated for a while about which measure of money Bitcoin most closely approximated; but M2, M3, and so on are all for debt-based currencies, so I agreed with Finney that M1 was probably the best measure.
21Million, times 10^8 subdivisions, meant that even if the whole word's money supply were replaced by the 21 million bitcoins the smallest unit (we weren't calling them Satoshis yet) would still be worth a bit less than a penny, so no matter what happened -- even if the entire economy of planet earth were measured in Bitcoin -- it would never inconvenience people by being too large a unit for convenience.
Source:
Why 1BTC should equal 10^8 satoshi ?This should more or less answer the first question
What is the logic behind having so many decimal places for cryptocurrencies like btc and ethereum
How is it decided for a new crypto, does it depend on coin supply
Pretty sure there is, off the top of my memory I can't remember one but you can create an ETH based ERC20 token without decimals so there's that
