I spent my first 20 years trying to be as accurate as I could be in cutting and piecing. It didn't even occur to me to measure or trim subunits for some time...
I've spent the last 20 years developing techniques where I cut larger and trim down. I find that in the end my results come out better, and even with the extra strep(s) are faster and more joyful/less drudgery. I also pin and press open, and use strip piecing techniques whenever I can. If I need to for complex shapes or steps I will make templates of the subunits. Warning, don't use template plastic as a cutting guide. Position the template and ruler to determine trim lines, and pull the template out of the way. Sometimes I will mark cuts/shapes with quilter's tape (1/4" masking tape) or blue tape on my ruler. With my vision issues I do this a lot.
I don't always cut large, for example, if I have to make a bunch of identical 4-patches, the strip piecing is usually enough. That is I take two WoF strips of fabric and sew them together first. Then I cut 2-patch pieces instead of starting with 2 piles of squares. When the 4-patches are made and pressed they do a quick under the ruler to make sure they aren't skewed and trip off any little bits if they are.
When cutting large there is no one rule that will work for "how large", the geometry and squares and trigonometry of triangles don't always play together unless you enforce some discipline
I want to cut large enough to be worth trimming without wasting fabric, usually 1/4" is more than enough. I have found I actually have very little waste, most of it is the 2-3" of leftover in strip piecing techniques. Despite the math and 7/8ths for a triangle tip, I always round up to a full inch. 1/8th may not seem like a lot but with two pieces of fabric, each 1/8th larger that is a 1/4 in total to trim off. Some shapes like a Flying Geese unit I cut the large triangle as directed, and just cut the side wings larger. For small HST I am more successful using what I used to consider a "fabric wasteful" technique of starting with squares and sewing along the diagonal line, cutting off and "wasting" the seam side. Again, I am faster and more accurate and small triangles use up lot of fabric in the seams as it is.