Webhooks would significantly reduce the read load I put on the API. Currently I read lots of data from many of the API’s collection endpoints every 30 minutes (reducing to every 10 minutes soon). If webhooks existed I would only need to bulk-read each resource once, and from then on I could just listen to the webhooks for changes.
While it’s always nice to do existing things more efficiently, I’m much more excited at the prospect of webhooks for deletions. The API doesn’t provide a way to find out what’s been deleted in FreeAgent (as has been noted here before 
) and there isn’t a neat way to derive it either. My system not knowing that a resource has been deleted in FreeAgent generates a steady stream of support requests for me from my users. Deletion webhooks would be a whole new capability rather than a variation on existing capabilities.
After deletion webhooks, the most useful one for me would be hearing when new bank transactions have been created. Most of the things my system does revolve around explaining bank transactions and it would be nice to be able to do that as soon as transactions appear in FreeAgent, rather than at the next scheduled sync.
Thanks!