By specifying a Minimum Balance for a Sweep Transfer (eg. $1,000) and a Frequency (eg. Monthly), Astra will transfer any funds OVER that minimum balance every month.
Say your balance is $1,234 on the transfer date. Your Sweep Transfer will be $234. But if your balance is $999, the transfer will not run that month.
The benefits of "sweeps":
Sweeps calculate the amount to transfer dynamically based on your current balance and run on your desired schedule.
Sweeps don’t overly “stretch” your account balance if you have a short term dip in funds on hand – if your balance is less than the minimum you specify, nothing happens.
If you have fewer expenses within the recurring time period (well done!), sweeps will transfer more money which can outpace a simple recurring transfer.
Read more about Sweep Transfers in this Article from the Astra blog.