Another Thing I want to add:
no matter if you use circulars or straight needles: you may make stuff that is longer than that needle at one point or another.
While the stitches then get bunched up along the needle and the top of your piece does not lie flat... what's the trouble?
you can work with your needle, unless the stitches themselves do not fit (that is when you can not compress them, yarn sling by yarn sling).
Let's say your needles are 10 inches and the thing you want to knit is 20 inches: no problem, mostly. The stuff will fit. If you have needles of 5 inches long... that is another story, really. It will get cramped at some point.
The other thing I want to say: I do not use straight needles and since childhood days did not use them anymore. I work with circs or dpn, depending on the project. But all my straight knitting is done on circular needles. I just do not want the leverage and angeling of the long needles. They get in my way and the weight of the knitting pulls on me funny. My grandmother solved her pain issues with knitting about 25 years ago when switching to circulars and I followed along, understanding about the beauty right away, even though I was still little. If you perfer straight needles: that is perfectly alright, as well.