ref: finish exp apply Desc

content/docs/command-reference/exp/apply.md

@@ -1,7 +1,7 @@
 # exp apply
 
-Apply the changes from a previous [experiment](/doc/command-reference/exp) to
-the <abbr>workspace</abbr>.
+Apply the results from any [experiment](/doc/command-reference/exp) to the
+<abbr>workspace</abbr>.
 
 ## Synopsis
 
@@ -15,12 +15,19 @@ positional arguments:
 ## Description
 
 Rolls back/forward the workspace to reflect the results of a given `experiment`
-(name or hash, see `dvc exp run`).
+(name or hash are accepted, see `dvc exp run` for details). This means changing
+the appropriate [metafiles](/doc/user-guide/project-structure),
+<abbr>parameter</abbr> files, <abbr>metrics</abbr>, <abbr>plots</abbr>, and
+corresponding DVC-tracked data.
 
 > This is similar to `dvc checkout`, but for `dvc experiments`.
 
-This is typically used before committing an experiment to Git, in order to make
-it [persistent](/doc/user-guide/experiment-management#persistent-experiments).
+This is typically used after using `dvc exp show` or `dvc exp diff` to find the
+best experiment, and before committing to Git in order to make it
+[persistent](/doc/user-guide/experiment-management#persistent-experiments).
+
+Note that this command will fail if the target `experiment` was not derived from
+the current Git commit.
 
 ## Options