You can throttle a Robocopy to avoid consuming all available network bandwidth by using the /ipg:n switch. This can be helpful if you need to perform a large data copy over a WAN.
To determine the inter-packet gap value to use for n, use the following formula:
D = (Ba-Bd) / (Ba*Bd) * 512 * 1000
Where Ba is available bandwidth in Kibibytes and Bd is the desired bandwidth in Kibibytes.
Also here is a handy calculator to help you test your values.