Making welting/piping

[Rudi50]

I am just recovering some dining chair seats. I'd like to add some welting. I've read that I should cut my fabric on the bias for the welting, but what if the fabric is patterned and it would look funny cut on the bias. What is the problem with just cutting it along or against the grain and which would be the better alternative, along or against the grain, if either?

[Joys Shop]

You can cut it straight if you want
but
cutting it on the bias can be a decorative element  (if you wish)

If you don't like that look,

go ahead and cut it straight