My stash boxes are 2 sizes of triangles, 2 1/2" and 3". They certainly don't have to be cut perfectly since they end up being squared up anyway.
When I sew 2 triangles together, I always chain piece with the dark consistently on either the bottom or top. That makes it easy for pressing. When pressing I put the long chain down with the dark on top, press to set, then flip and press one after another, usually using sizing. THEN I cut apart. \
Next is the squaring up. I dearly love my square-up rulers. I love the Quilter's Rule one because the markings are raised in the back and the diagonal nests right in the seam. In fact I have gone through several because after time, the markings wear off and the corner shaves off.
I have this square ruler also in blue for dark fabric and love my 12 1/2 " also.
I honestly don't mind squaring up. I'd do that for an hour gladly compared to sewing on borders for an hour! It is absolutely essential that all pieces are squared up, by the way! Here are a few examples of quilts I've done using triangles. As you can see, I've done a LOT of triangles!
|Churn Dash is a fun square/triangle block|
|Jewel Box--Good for squares and triangles|
|Mom and Dad's Anniversary quilt|
|Wedding memory quilt|
|Gosh I love stars!|
|I love stars!|