making sense of commit_preserve_order in a logical standby

I'm trying to make sense of this statement about commit_preserve_order

"SQL
Apply uses this as the default mode because reporting applications often require strict transaction ordering between the primary and standby databases.
Optionally,
for increased performance, transactions can be applied in a different order than on the primary database, but transaction consistency within each transaction is always maintained after switchover or failover. Following a role transition, the new primary will be consistent and will contain all transactions up to a specific time or SCN. If this is acceptable for your application and increased performance is your goal, then consider the following change:"

My understanding of this means we will keep transaction consistency but not wait for commit approval and just go forward.

My question is what is the strict ordering oracle is talking about

i.e
an example application picks up all data that was generated before midnight . The timestamps and all the data is coming thru from the primary. commit_preserve_order=True vs commit_preserve_order=false what will change.

Fuad Arshad

--
http://www.freelists.org/webpage/oracle-l