This displays the number of data requests per second that the software is currently making to Betfair's API server when using Polling for requesting price data. Previously, you were only allowed to make a maximum of 20 requests per second with requests above 20 per second being subjected to a Data Request Charge.
With the introduction of API-NG (Betfair's new API), the Data Request Charge was scrapped.
There is still a restriction which is that you only allowed to make a maximum of 5 price refreshes per second per market.
So you no longer need to be concerned with this, the figure has been left in place for information only.
The figure in brackets displays the number of requests that have been made above the 20.
It is now safe to disable the throttling of excess requests which you can do in Preferences under Throttling.