Stat Table vs Automate Gather Statistics

There are two distinct approach for statistic gathering in oracle :

Manual Stale statistics gathering

Automate statistic gathering (default)

I have two queries:

1. Need to understand what should be the conditions to decide upon use of methods define above ?
2. if we keep statistics in stat table and lock those statistics to be get used every time for particular db objects. what could be the conditions where this method can be use?

As per my understanding :

1. Where data deletion/insertion and update is like OLTP systems and very frequent. we can use manual statistics gathering.
2. & where data is not much changing and use just for reporting purpose just like data warehouse, we can use automate statistics gathering.