Hi MattM - Our organization (Missouri Small Business Development Center) sends out relationship surveys to a random sample of clients semi-annually. We have tried quarterly as well. We have enough of a database to warrant this, but do not have the manpower to analyze and implement changes frequently enough for it to be useful. Our local center supplements with a different survey every 18 months to our entire population of clients.
The main things I would consider in deciding the frequency:

1. How large of a client/customer base are you sending to? The larger your list, the easier it is to justify sending more frequently.


2. Are you sampling or sending to everyone? Customers/clients easily suffer from survey fatigue if asked too often. This is especially true if you are also sending transactional surveys.


3. What are you doing with the data? Data for data's sake is not beneficial. Make sure you have the resources to learn from the data and implement changes.

https://www.qualtrics.com/community/discussion/comment/32265#Comment_32265Thanks LRCoffman
I'm always wary of survey fatigue, but I hope and trust that getting an invite for a larger survey twice per year will not be too much. Especially since I'm trying my best to display and highlight the changes coming from the feedback we receive. So it's not just "data for the sake of data". We're actually driving several work streams in order to improve where we can and unless that's highlighted they'd never know.
Again, thansk for the feedback!
-Matt