Definitely random. You should see my workroom! I made a system for using the "scraps", which are more like the size of fat quarters. I grab from one small tub to use and place it in another tub. When original tub gets low, I switch. However, somehow I have about 4 different tubs at the moment, And, I've even trimmed 3" or so from new fabric to use! I tried to avoid white and black.
I have a 6.5" clear Dritz ruler that has been extremely functional when trimming. It is 1/4" thick, so I lay it where the strip looks best, then use washable marker to draw cut/trim line to the outside edge, and the ruler allows for SA. This allows me to be picky about which part of the scrap shows up.
https://www.amazon.com/Dritz-862-Sup...38&sr=8-3&th=1
I also use the clear ruler on the first "triangle" to trim excess from second triangle's side, leaving only 1/4" extending into the area. I'll go take a close up pic of one finished block. I hope to make the final 3 blocks today!