We said we were discussing (a) certain matter then.

The sentence with/without the indefinite article "a" before the word "matter" is grammatically correct, depending on the sense the word matter is used.  "Matter" is used both as a countable noun and uncountable noun.
When you use it as a countable noun to refer to a situation or subject someone needs to deal with, you should use "a" before it.  

On the other hand, when you use "matter" as an uncountable noun in the sense of substance, material, it doesn't need "a" before it such as we discussed certain printing matter.

"discuss certain matter" is there any mistake in this sentence?
From the perspective of a Ph.D. student, how much of an added value is it to have your own presentation slides layout, that is used consistently throughout your Ph.D. conference presentations and other talks (and possibly throughout your academic career afterwards)?

Here is one such example from the Computer Science community.

This as as opposed to using existing Beamer templates with LaTeX, or built-in PowerPoint templates, or simply preparing each presentation on its own (without a specific layout).

A couple of axes I can think along:


Creating a signature layout that distinguishes one in their community
Ease of preparation of presentations (especially over time), maybe overcoming constraints with existing templates.


Note that I am not concerned with the question of content, but just design and layout.
