For the Cryptonote coins, they have 12 decimal place for the coins, is it necessary? Is it better to increase the total number of coins by 10000  times and remove 4 decimal places?  Would that decrease the block size?

One recent block reward of XMR is 13.828558554977, if we remove the last 8 digit, so that it is 13.8285. That will remove the dust and that value is still close to the original one, the difference is only 0.0001/13.