Intuitively it seems reasonable to say that you only need the extra battery life if you frequently let your battery run out (implying you do not charge often enough, or long enough). So, how often do people recharge their phones? Is this a problem many people encounter? You might find the 2011 paper by Ferreira et al. interesting. It is titled "Understanding human-smartphone concerns: a study of battery life". They were interested in the recharge behaviour/patterns of smartphone users.
I will quote some parts from the paper as it applies to your question, but you should really read the full paper to get a more complete answer.
Some context from the abstract:
This paper presents a large, 4-week study of more than 4000 people to
assess their smartphone charging habits to identify timeslots suitable
for opportunistic data uploading and power intensive operations on
such devices, as well as opportunities to provide interventions to
support better charging behavior.
How do users manage batter life?
Users mostly avoided lower battery levels, with the daily average of
the lowest battery percentage values being 30%. This is likely due to
the fact that the Android devices’ battery icon turns yellow at 30%,
and prompts the user with a textual notification to charge the
smartphone by the time it reaches 15%.
How do people fit "charging time" into their daily routines?
The data reveals two major charging schedules: one between 6PM and
8PM, with the majority of users initiating charging when the battery
levels are at 40%, and another charging schedule between 1AM and 2AM,
with a majority initiating charging when battery is at 30%.
What counts as "charging time"?
By charging time, we mean the time since the user plugged his device
to charge until unplugged from the outlet.
How long do people typically leave their phones to charge?
The majority of the charging instances occur for a very small period
of time (up to thirty minutes) or between one to two hours, which is
the average required time to recharge completely a battery.
however, some people leave the phone plugged in
As expected, a lot of charging instances happen overnight, for 14
hours or more...
How do people charge their phones?
As predicted, for longer charging periods AC is the preferred choice
for phone charging. For short charges (30 minutes or less), USB
charging is much more frequent. On average, users charge their phones
39% of the time using USB, and 61% of the time using AC...
So, it seems that most people won't necessarily benefit from 9% reserve battery power, given the typical power-management behaviour. The one caveat is what constitutes a "typical user"...