I just spent 20 minutes chatting with my project manager about client-related work, but it wasn't technically billable. Yet, during that unbillable time, I came up with an idea that I'll present to my client on a call tomorrow.
Can I bill those 20 minutes to the project budget? When we opened our mouths to have that conversation, it wasn't our intention to do "billable" work. We were simply staying in touch on the progress of the project, and my PM just wanted to let me know that he agreed with the POV I provided to the client on an email.
There are many reasons against slavishly and unblinkingly worshipping at the altar of the Billable Hour. This is one more.
Serendipity is the vital life blood of creativity and innovation.
It's simply impossible to capture within a rigid observance of the billable-hour construct. I'm not saying that the billable hour is absolutely useless as a business metric. It's just that I've seen it best implemented as part of a holistic set of metrics rather than be chased as the holy grail.