I am more inclined to trim small units (tiny hourglasses match up better if they're trimmed, for example) and final blocks than I am to trim part way through a complicated block. On my most recent quilt, many of my house blocks were "trimmed" but still ended up with gaps in what should have been straight edges because my FG units (the roof of each house) were quite unpredictable (and frequently really off). The trimming did help me be aware of which areas would need to be sewn more carefully to the sashing to maximize the strength of places where the seam was reduced to closer to 1/8" because of these weird blocks. I think that was the most helpful part of the trimming process for me. :-)