Oh, BTW I read last week that ubuntu still uses bash for user shells, but
uses dash as a lighter, faster shell for "system stuff".  I am not sure what
that means other than /bin/sh links to /bin/dash because if I open a
terminal and look at my env, it shows SHELL=/bin/bash.

The only other aspect I am aware of is if you run a script that opens with
#!/bin/sh, you will be running dash, not bash.