Squaring up

[rubywishes]

I always square my fabric before cutting my WOF but what about if I I am cutting LOF? How important (or possible)is it?

[BrendaP]

If you have squared the uncut fabric it will be square regardless of whether you subsequently cut LOF or WOF.

[Lowena]

Gosh you are a perfectionist Rubes....I've never given it a thought 

[rubywishes]

Oh good grief @BrendaP .......what a dill I am LOL! Sometimes I amaze myself with my numptiness! Now excuse me while I take a rather long rest behind the sofa.......quack!

[Deafoldbat]

I've never given it a thought 

Well, next time you can't sleep....

As it is rolled onto the bolt, the fabric will move about a bit. If you unfold the piece you bought you'll probably find the cut edge isn't exactly at right angles to the selvedge. Unless you realign the fabric - easier to do if you've washed it - then any wof cut will be off grain. This isn't necessarily a total disaster, but getting the grain straight reduces fraying and stretching.
Cutting parallel to the selvedge will give you on-grain strips and less chance of stretching.