I just found out the optional parameters, and I fell into confusion.
Considering the two following examples:

• [routerLink]="['/any-uri', {key: value}]"
• [routerLink]="['/any-uri']" [queryParams]="[{key: value}]"
  In what circumstances should I use optional parameters instead of queryParams. Is there a rule/good practice?

I found several docs for the how, but none for the why/when.