aftermarket radio wiring issue (grounding)
 

I wonder if anyone on this forum has any experience with aftermarket radio installation, specifically about grounding the new radio.
Car model: Accord
Year: 1999
What has been completed:
connected a commercial wiring harness adapter to the wiring harness (black to black grounding wiring) for the new radio. The commercial harness adapter then connecting to original factory wiring harness. No additional "grounding".

I am getting some conflicting info so not sure what is necessary and what is not -
For most postings on the internet, people talk about grounding the new radio, NOT through factory original grounding line, but through a new entry to the car chassis. However, a few other postings say (a) Japanese cars have a metal case to host the radio so they are grounded that way; (b) on installdr.com it says "Connect the GROUND wire of the new radio to the ground wire of a snap on wire harness".

So the question of the day: DO I need an additional grounding of my wiring to the car chassis ?? Any info will be appreciated. Thank you for reading.