Clarify docs for ALTER TABLE EXECUTE

docs/src/main/sphinx/sql/alter-table.md

@@ -54,13 +54,18 @@ per-connector basis.
 You can use the `=>` operator for passing named parameter values.
 The left side is the name of the parameter, the right side is the value being passed.
 
-Collapse files in a table that are over 128 megabytes in size with the `optimize`
-procedure from the [Hive](hive-alter-table-execute), [Delta
-Lake](delta-lake-alter-table-execute) , and
-[Iceberg](iceberg-alter-table-execute) connectors:
-
-```
-ALTER TABLE hive.schema.test_table EXECUTE optimize(file_size_threshold => '128MB')
+Executable commands are contributed by connectors, such as the `optimize`
+command provided by the [Hive](hive-alter-table-execute), [Delta
+Lake](delta-lake-alter-table-execute), and
+[Iceberg](iceberg-alter-table-execute) connectors. For example, a user observing
+many small files in the storage of a table called `test_table` in the `test`
+schema of the `example` catalog, can use the `optimize` command to merge all
+files below the `file_size_threshold` value. The result is fewer, but larger
+files, which typically results in higher query performance on the data in the
+files:
+
+```
+ALTER TABLE example.test.test_table EXECUTE optimize(file_size_threshold => '16MB')
 ```
 
 ## Examples