Some people want the automation.
And if you are going long term and doing a DCA, it is recommended to just do a fixed day conversion and ignore timing for the best exchange rate.
The same like you ignore the "best" price to purchase monthly. Just execute on a fixed day.
Just my 2 cents.
I can see the appeal of letting a fixed conversion instead of timing the currency conversion for convenience sake...I just changed the currency as I feel at that time that the USD is quite cheap and I saved a few SGD...I think it is more of me testing how FSM works that's why you see me depositing, converting and withdrawing from FSM...
Since I am paid in SGD, I would rather set a budget in SGD and convert the amount to USD as it wouldn't make sense for me to set the amount in USD and have different amount being deducted from my bank account each month...I would rather set how much SGD I want to change to USD and change my USD investment amount...
Just my 2 cents...