The amount of usage doesn't seem to matter in my testing. I didn't share anything (and I also set the discoverable setting to 'no one'), and I see a big difference in the throughput: 38 Mbps (awdl0 interface up) vs ~80 Mbps (awdl0 interface down). Yikes. This was a TCP test using iperf, between the laptop and another machine on the lan.

Turning off bluetooth didn't help, so it looks like it's easy to be affected by the performance hit.