Effect of creating missing index

From AWR report of one OLTP database, I identified three missing index based on top buffer gets and physical reads. After creating them with eager, the outcome is tremendous to me -almost improved 100%.

Comparing Period: 3pm ~ 6pm of 8-May and 9 -May (in seconds)

DB Time (=response time?) : 39317s -- > 20526s (database become less busy)
Service Time: 23709s --> 10767s ( less CPU time)
Wait Time: 15608s -- > 9759s (DB Time - Service Time)
Buffer Hit Ratio: 75% --> 89% (some more to tune)



TIP
Tuning the top 25 buffer get and top 25 physical get queries has
yielded system performance gains of anywhere from 5 percent to
5000+ percent in my tuning. The SQL section of the STATSPACK
report tells you which queries to consider tuning first. The top 10 SQL
statements should not be substantially more than 10 percent of your
buffer gets or disk reads.