Hi there,
Who told you that? 
LOL, No this is NOT true, You certainly can. things like Logging output and Debugging output are both possible. On the expansion board when plugged in Shows up in the Serial ports (monitoring on the SDK terminal) or as I do Use the Serial terminal program in the Nrf_connect for Desktop Programs.
See the White Cable., It’s all in what you do and learn.
Start A New thread or resurrect an older one related to this topic.
I have a couple on here, some of which is covered, but worth revisiting. This one has gotten off track but good stuff none the less, Folks can bookmark it for future reference.
You can do a lot with the Xiao Expansion brd. it’s a foundational building block, connected to a external Debugger is were the true power of these devices and connections show themselves. Speed in development and Quick diagnosis for undocumented enhancements (Bugs) make them worth every P&J for lunch instead of Char-Hut and other side hustles makes saving , acquiring and owning such tools a pleasure to do WORK!
HTH
GL 
PJ 
You should know these things if you plan on doing ANY real productive work with this stuff IMO. start there. 