Good points, Bear! I came back to say that you will really notice how different Trigonometry is to normal Geometry when you start turning back those triangle seams.
You can have as much fabric on the back of a small triangle as the front and with the half-inch seam you will notice it and maybe even have to trim them down sometimes.
When I started, 1/4" seemed so amazingly tiny, after years of looking at it even with my declining vision issues, I've decided it's actually pretty darn big compared to the size of thread. By now, some 20 years of rotary cutting the translations of design size+ 1/2" of seam allowance has been driven into me and I just know that the math is to add 7/8ths to the finished size of a right triangle instead of the normal 1/2". I sort of have a mental chart of finished to full sizes in my head.
But I do get confused all the time and I will write out cutting instructions for me, currently there is a computer monitor set up on the other side of my cutting mat and I bought a sticky pad just exactly to use for my cutting notes and I stick it square in the middle of the screen. Sometimes not until after I've already botched stuff up! But I do try to go through my math and make sure what I'm doing is correct. Sometimes I use junk mail and cut it and play with it first, just to make sure.