chore(docs): updated info about hook scripts

docs/dcc-tables.md

@@ -45,7 +45,7 @@ The loadtype determines the nature of the update to be applied. Valid values are
 This is a required field.
 
 !!! Note
-    The support for BITEMPORAL loads is restricted, in the sense it is only possible to load data at a single point in time (no support for loading _multiple_ business date ranges for a _specific_ BUSKEY). The workaround is simply to load each date range separately. As a result of this restriction, the EDIT page will only show the latest business date range for each key.  To modify earlier values, a filter should be applied. 
+    The support for BITEMPORAL loads is restricted, in the sense it is only possible to load data at a single point in time (no support for loading _multiple_ business date ranges for a _specific_ BUSKEY). The workaround is simply to load each date range separately. As a result of this restriction, the EDIT page will only show the latest business date range for each key.  To modify earlier values, a filter should be applied.
 
 ### BUSKEY
 
@@ -108,7 +108,11 @@ If your DQ check means that the program should not be submitted, then simply exi
 
 ### PRE_APPROVE_HOOK
 
-[Hook script](#hook-scripts) to execute before the approval diff is generated. It can be used to modify the values presented to an approver on the approve screen.  This can be helpful in order to present the data in way that can be easily consumed by approvers.
+This [hook script](#hook-scripts) will execute twice during a typical workflow - firstly, before the approval diff is generated, and again after the approval (not rejection) and _before_ the change is applied.
+
+This makes it a helpful place to prevent changes being made, eg in situations where the target table needs to be locked by alternative systems.
+
+It can also be used to apply display formats.
 
 Leave blank if not required.
 
@@ -119,13 +123,13 @@ SAS Developer Notes:
 
 ### POST_APPROVE_HOOK
 
-This [hook script](#hook-scripts) is `%inc`'d _after_ an approval is made. This is the most common type of hook script, and is useful for, say, running a SAS job after a mapping table is updated, or running a model after changing a parameter.  
+This [hook script](#hook-scripts) is `%inc`'d _after_ an approval is made. This is the most common type of hook script, and is useful for, say, running a SAS job after a mapping table is updated, or running a model after changing a parameter.
 
 Leave blank if not required.
 
 SAS Developer Notes:
 
-At the point of running this script, the data has already been loaded (successfully) to the target table. Therefore the target is typically the base libref.table (or format catalog) itself and can be referenced directly (YOURLIB.YOURDATASET), or using either of the following macro variable: 
+At the point of running this script, the data has already been loaded (successfully) to the target table. Therefore the target is typically the base libref.table (or format catalog) itself and can be referenced directly (YOURLIB.YOURDATASET), or using either of the following macro variable:
 
 * `&orig_libds`
 * `&libref..&ds`
@@ -142,11 +146,11 @@ If you are making changes to the target table as part of the hook, then in order
     ref=Locking table to peform a post approve hook action
     ctl_ds=&mpelib..mpe_lockanytable
   )
-  
+
   /* do stuff */
   proc sort data=somelib.sometable;
   run;
-  
+
   /* unlock */
   %mp_lockanytable(UNLOCK,
     lib=SOMELIB,