All of these workflows are a “it depends” scenario. If what you do works, then stick with it! Considerations:
Transcode before editing is usually considered because codec being referenced takes a lot of processing to decode and editor wants to do more in real time when it comes to layers, VFX, multicam, etc. or working in a shared storage environment.
Some productions like having a smaller proxy codec like DNxHD 36 that still looks good but can play off a FireWire drive and still be projected on a 40 foot screen if needed. Lots of storage for mobile use, etc. 65 hours on a single 1 TB drive for example.
Some back end exports do not work with AMA linked media such as QuickTime reference, etc. If you are exporting a self contained format then MC is doing a render in the background anyway which is why it will work. Many productions like to use “same as source” as either ProRes or DNxHD and will transcode sequence to one of those then export as such.
Lots of reasons why a production chooses one over another – the key is to find the one that works for you.
Michael