I try and keep my cables relatively tidy for practical purposes - as ethics says it depends on how tidy you want them to be, and for what reason (I know some people spent considerably longer tidying their cables than I spend building the whole machine).
If you just want it for practical purposes I would suggest trying to power the Hard drives from one cable (assuming 1 or 2 drives), and optical from another, then using cable ties (reusable ones are best) to hide the excess cables in a 5.25 inch bay if you've got one spare (or behind the 3.5" bays depending on case), also try and run data cables discretely, and in the order in which the are used/most likely to need moving again (hide use cable ties or similar to hide them in unused bays, but leave enough spare so you can unplug them if needed).
The main benefits of tidying them up, if you don't want them to look pretty

, is to increase airflow a bit, and make it easier to find the one you want

(I often either use small stickers or write directly onto cables with what they are for, at both ends*).
Fortunately we are now (generally) past the days of large ribbon cables, so it's much easier to tidy them up now, despite often having more drives than in the past
*I tend to have 3-4 hard drives (of varying sizes) in my machines (to allow me to have multiple copies of important files, and because i'm loathe to throw them out

), so having the cable marked as "boot", "backup" or "DVDRW" is handy when I need to unplug a drive or whatever.