Q:

Does order of indexing (ascending vs descending) matter? 

Some said for compound indexes then ordering matter.  Some says ordering doesn't matter. 
Which one is right?  And why? 
I mean if I look up phone, I don't see how whether the phone is sorted a to z or z to a matter at all.  How would that change for compound indexes? 
Note: What i mean is ordering in descending or ascending sense.  I am well aware that ordering of the column matter. 
Note we have 2 answers by high point members.  One say that descending or ascending doesn't matter even for compond index.  Another said it matters.  So yes there is controversy here.  Where can I (or we) dig more. 

A:

Ordering in the general case does matter.  The question is: What ordering are you referring to and does it matter in your case? 

Descending vs Ascending.  Matters only in very special cases where you actually want the result sorted in a special order.  Say you want your result ordered like this: 
a asc, b desc, c asc

but your index is 
a asc, b asc, c asc

The database has to do an additional sort.  The same applies when you want to access the first n elements according to some order.  This is more important for composed index, because a change of direction of a single column results in a completely different total ordering, while the ordering of a single column in a single column index just reverses the ordering. 

Ordering of the columns so
a, b, c

vs 
b, a, c

If you filter for all columns it doesn't make much of a difference, but if you filter only for a, the first index will be more useful than the second.  
Whenever you have two options for solving a problem in a programming language and somebody tells you they don't make a difference, ask why the two options exists.  If 'somebody' can't answer that, I wouldn't trust his advice on the two being equivalent.  

A:

I think the confusion is based on two different meanings of "ordering". 

Whether the indexed items are sorted in ascending or descending order. 
In a compound index, which column is used first to sort the items

The first one, as you mentioned, does not matter.   The second does matter, though.