DOC-5508: Added description of XDCR desired latency (#1066)

* DOC-5508: Added description of XDCR desired latency

* DOC-5508: typo

* DOC-5508: Minor rewording

Co-authored-by: Tony Hillman <tonyhillman@Tonys-MacBook-Pro-2.local>

modules/rest-api/pages/rest-xdcr-adv-settings.adoc

@@ -262,7 +262,12 @@ For information, see xref:xdcr-reference:xdcr-advanced-settings.adoc#table-of-xd
 
 | `desiredLatency`
 | Integer
-| Default: 50.
+| Specifies the amount of time in milliseconds within which a high-priority replication's currently remaining changes should be reduced in number to zero, by ongoing transmission of the changes from source to target bucket.
+If Couchbase Server estimates that the time required is greater than that specified by `desiredLatency`, the replication is considered to be backlogged: XDCR therefore attempts to communicate with the Data Service, to establish a higher DCP priority for the replication, and thereby ensure swifter transmission of data.
+
+This setting applies only to high-priority replications, or to medium-priority replications that achieve high-priority status (see xref:learn:clusters-and-availability/xdcr-overview.adoc#xdcr-priority[XDCR Priority]).
+The default value is 50.
+The lower the value, the higher (potentially) the transmission rate, and the greater the load on the target cluster.
 
 | `docBatchSizeKb`
 | Integer (10 to 10000)