When I first started quilting, I did not know (care) about trimming blocks when putting them together. The patterns I used did not mention it. However, after wrestling fabric into a top and losing, I started trimming. For HSTs, the Bloc Locs were wonderful. For squares, the Stripology Ruler makes it work. I am on the last round for another exploding squares quilt. I started with 4" squares. The last squares is 8". I trimmed every sewn square before I put on another square.
My mom can sew the 4 edges, but I cut them open and trim and layer. I use washable Elmers glue in the 4 corners to hold the layers so there are no pins and so my speed demon mother cannot get them out of whack in the corners (I keep saying they are FEED dogs, not PUSH dogs to no avail).
Anyways, I gave her the last round on Thanksgiving and you can see the slight slivers of fabric left which make a huge difference when I sew the blocks together (will need another last trim).