From the online help...

• WSGRACESLOWDOWN describes the rate used to decrease the speed of the web services between the size limit and the size limit plus the grace limit. If for instance the value of this parameter is 5, it means that once the 1 Mb limit has been reached on a given day, the speed will be divided by 5 until the limit of 1.1 Mb is reached within the end of the day (if this limit is reached, the web services will stop).

https://online-help.sageerpx3.com/erp/9/staticpost/soap-web-services-implementation/?highlight=WSGRACESLOWDOWN+

It is a SOAP Web Services licensing control as mentioned by Stephen. It's not new, it's been there since PU9 released in 2015.

However, SOAP Web Services are not billable since V7, so if you need more SOAP Web Services and your license is not enough or slowing you down, then you can request an extend of the limits, which by default are 1 GB per day I believe, which is normally more than enough for any integration.