Adding more information about configuration neo4j#539 (neo4j#547)

Cherry-picked from neo4j#539

Author: lidiazuin

modules/ROOT/partials/neo4j-config/all-settings.adoc

@@ -278,7 +278,8 @@ If this is set to `false` (default), the search for group membership will be per
 |<<config_dbms.transaction.sampling.percentage,dbms.transaction.sampling.percentage>>|Transaction sampling percentage.
 |<<config_dbms.transaction.timeout,dbms.transaction.timeout>>|The maximum time interval of a transaction within which it should be completed.
 |<<config_dbms.transaction.tracing.level,dbms.transaction.tracing.level>>|Transaction creation tracing level.
-|<<config_dbms.tx_log.preallocate,dbms.tx_log.preallocate>>|Specify if Neo4j should try to preallocate logical log file in advance.
+|<<config_dbms.tx_log.preallocate,dbms.tx_log.preallocate>>|Specify if Neo4j should try to preallocate the logical log file in advance. 
+It optimizes the filesystem by ensuring there is room to accommodate newly generated files and avoid file-level fragmentation.
 |<<config_dbms.tx_log.rotation.retention_policy,dbms.tx_log.rotation.retention_policy>>|Make Neo4j keep the logical transaction logs for being able to backup the database.
 |<<config_dbms.tx_log.rotation.size,dbms.tx_log.rotation.size>>|Specifies at which file size the logical log will auto-rotate.
 |<<config_dbms.tx_state.memory_allocation,dbms.tx_state.memory_allocation>>|Defines whether memory for transaction state should be allocated on- or off-heap.
@@ -624,7 +625,8 @@ If this is set to `false` (default), the search for group membership will be per
 * <<config_dbms.transaction.sampling.percentage,dbms.transaction.sampling.percentage>>: Transaction sampling percentage.
 * <<config_dbms.transaction.timeout,dbms.transaction.timeout>>: The maximum time interval of a transaction within which it should be completed.
 * <<config_dbms.transaction.tracing.level,dbms.transaction.tracing.level>>: Transaction creation tracing level.
-* <<config_dbms.tx_log.preallocate,dbms.tx_log.preallocate>>: Specify if Neo4j should try to preallocate logical log file in advance.
+* <<config_dbms.tx_log.preallocate,dbms.tx_log.preallocate>>: Specify if Neo4j should try to preallocate the logical log file in advance. 
+It optimizes the filesystem by ensuring there is room to accommodate newly generated files and avoid file-level fragmentation.
 * <<config_dbms.tx_log.rotation.retention_policy,dbms.tx_log.rotation.retention_policy>>: Make Neo4j keep the logical transaction logs for being able to backup the database.
 * <<config_dbms.tx_log.rotation.size,dbms.tx_log.rotation.size>>: Specifies at which file size the logical log will auto-rotate.
 * <<config_dbms.tx_state.memory_allocation,dbms.tx_state.memory_allocation>>: Defines whether memory for transaction state should be allocated on- or off-heap.
@@ -3828,7 +3830,8 @@ m|DISABLED
 [cols="<1s,<4"]
 |===
 |Description
-a|Specify if Neo4j should try to preallocate logical log file in advance.
+a|Specify if Neo4j should try to preallocate the logical log file in advance. 
+It optimizes the filesystem by ensuring there is room to accommodate newly generated files and avoid file-level fragmentation.
 |Valid values
 a|dbms.tx_log.preallocate, a boolean
 |Dynamic a|true