Providing a routing url when publishing a subgraph

I was wondering why you should not provide the routing url again after you first publish a subgraph.

The --routing-url parameter description states:

Optional after your first publish. Provide only if you need to change the subgraph's routing URL.

But what is the downside of providing it every time you publish a subgraph again? Why should we avoid it?

It does seem to work just fine when you provide it every time for all your subgraphs. So, I don’t quite understand why this is recommended.