In a manuscript, how do you know when you need to source the brand and location for materials?

I'm writing my first manuscript and haven't received a lot of guidance on it. The journal that I plan on submitting to has an "Instructions for Authors" page, but I've scoured it and there is no information about sourcing the brand for your materials in the methods. I've looked at several articles from their most recent issue, and some but not all the materials were sourced.

Here's an example:

"...containing an aliquot of RT mixture (SsoAdvancedTM SYBR Green Supermix, Bio-Rad Laboratories Inc.)..."

How do I know which materials I should be sourcing in my manuscript? It doesn't say anywhere on the journal's information website, yet so far all the articles I've seen have done it.

(Also, why is this necessary? Shouldn't it be a given that if I'm using some industrial solution then it should be the same independent of the brand I use?)