The question that you brought up wouldn't address your question because "if" is not one of the coordinating conjunctions, but it is a subordinating conjunction. The words that introduce each are:
Coordinating Conjunctions: and, but, or, yet, for, nor, so (a helpful acronym is FANBOYS)
Subordinating Conjunctions: after, although, as, as if, as long as, as though, because, before,
even if,
even though,
if,
if only,
in order that,
now that,
once,
rather than,
since,
so that,
than,
that,
though,
till,
unless,
until,
when,
whenever,
where,
whereas,
wherever,
while
The definition of a subordinating conjunction is:
Subordinating Conjunction (sometimes called a dependent word or subordinator) comes at the beginning of a Subordinate (or Dependent) Clause and establishes the relationship between the dependent clause and the rest of the sentence. It also turns the clause into something that depends on the rest of the sentence for its meaning.
He took to the stage as though he had been preparing for this moment all his life.
Because he loved acting, he refused to give up his dream of being in the movies.
Unless we act now, all is lost.
This article from Purdue on coordinating and subordinating conjunctions explains the usage of the subordinating conjunction as follows:
Notice that when the subordinate clause comes at the beginning, it’s necessary to insert a comma.
From this, the correct punctuation of "You can call me if you need me" is:
You can call me if you need me.
If you were to move the subordinating conjunction to the beginning, however, you would need the comma as follows:
If you need me, you can call me.
Use a comma before non-restrictive clauses, and don't use a comma before restrictive clauses. See this webpage.
How do you know whether a clause is restrictive or non-restrictive? It's restrictive if the information is essential, and limits the scope of the thing it's modifying. It's non-restrictive if the information is non-essential. For both of your sentences, the clause can be analyzed as either restrictive or non-restrictive, so in cases like this, the comma is optional.
Best Answer
When you include the comma, the meaning of your sentence changes:
I entered the specific room which I knew would contain the hostages.
I entered a room, and I discovered the hostages in there.
To take one of your sentences:
If we add a comma before where, then we imply that in all congestion control mechanisms noisy feedback is averaged. Actually, we could leave out the whole where clause without losing relevant information (anyone knowing enough about the subject already knows that about congestion control mechanisms).
Without the comma, the extra information makes it clear that this does not hold for all congestion control mechanisms, but it does for the ones we are talking about. We cannot remove the where clause without changing the meaning of our sentence.