As Unity supports Rich Text tags, you use them in your Debug.Log
methods in order to liven up your Console window and put emphasis on important Debug lines. Whilst some Rich Text tags will be more useful than others in this context, some helpful examples would be Color, Bold, Italics and maybe even Size, depending on how you have your Console setup.

Here are some examples of Rich Text tags in use in code. A good idea would be to write extension methods for commonly used debug lines so that you don’t have to keep writing out the same tags.
Debug.Log($"This object's name is <b><color=white>{gameObject.name}</color></b>!");
Debug.Log("<color=green><b>Everything has gone okay!</b></color> <i><size=8>Hooray</size></i>");
Debug.LogError("<color=red><b>[ERROR]</b></color> - Something has gone wrong.");