Signal ground and chassis ground in OBDII port and gadgets that tie them together


I am trying to use Arduino Uno and Freematics OBDII adapter to make my own car gadget that reads car data and displays it on gauges and display, but I have encountered something that I want to clear out before proceeding. So the OBDII port has two grounds, chassis ground and signal ground. If I understand correctly, signal ground is from computer, is low noise and is used for CAN comms and stuff (in OBDII case), while chassis ground is for anything that requires reasonable amounts of power and is tied directly to car battery negative terminal. Also, the grounds are supposed to be tied together at some point by car manufacturer if everything is done properly. Here’s the thing, I read around that its not recommended to tie them together by yourself (yourself = at OBDII port) because you can cause ground loops and introduce noise to signal ground, but many gadgets (Freematics OBDII adapter included) do this - I assume then that its the right thing to do, or is is a “cheap” way out that can cause problems? I’m a bit puzzled, is it okay to proceed this way? I don’t want to cause car problems with my gadget. Any insights are appreciated, thanks!