My sisters say I am too picky but I always square up. I do it different ways - depending on how it is sewed.
If the pattern calls for 3 7/8 squares - I make them 4in.
Or I use triangle paper - Thangles or generic.
If I am working on basic 4-patch... 9-patch - I sew a scant 1/4 inch seam and square it up. Always...
I use a JuneTaylor - Shape Cut or her Perfect Half-square & Quarter-Square Triangles Ruler. One of my favorite/most important tool in my quilt room. I have worn out/cracked two two Shape Cuts - not because of poor quality but because I use them daily.
One of the reasons I am so picky is that sister got chewed out by her long arm quilter cause her quilt was so off square... Not me! My sister was a bit miffed but I just took note!