I think the answer to this would really depend on the exact nature of your role.
For instance, you can imagine how the answer would vary widely depending on whether you are:
1. Customer facing in the sense that you try to directly sell (B2B or B2C) a particular good/ service
2. Customer facing in the sense that you handle customer complaints / issues and try to resolve. In this case, there would be a lot of potential to improve processes and measures of both the metrics being reported and how they are measured, as well as the feedback from the most common customer pain points themselves to build a better product / offering.
The same answer can again be tailored depending on exactly HOW you are customer facing. Other possibilities could be:
1. After-market sales and add ons/ support
2. Implementation support - helping customers implement technology that they have purchased
3. Campaign management for new / improved products / services..
As you can see, the ways i which you could leverage the skills you obtain via a PMP certification would really vary depending on what you actually DO in your day to day role and how you could potentially add more value.
If you can provide more details, I am sure we can all chime in with more specific and relevant answers!
