Just to toss my feedback in the ring: I listen to a podcast themed around a local sports team on Spotify, and I often download them to my phone locally because I'm old and still have the habits of being on a limited data plan even though I've had unlimited for years.

I noticed the ads (pre-roll, mid-roll, and post-roll) and was surprised because a lot of them tend to be local ads for various cities across the US. HVAC services in Chicago, lawyers in Houston, etc. None for the city where the podcasters live, most of their audience lives, or the spots team is based.

I don't always download the episodes to listen, only if I know I'm going to be out , or if I'm mowing the lawn and might occasionally stretch my wifi range. I haven't tested fully, but it seems as though the ads only get baked into the audio upon download.

I also noticdd a few months ago that downloading a podcast I was partway through resets my progress, which has been incredibly annoying. If the ads are inserted at the time of download, that would make sense because the length of the audio would change.