A racking cane will allow you to "rack" or siphon from the top of a fermenter down, thereby not disturbing the trub any more than necessary. This is applicable to racking primary to secondary, primary to keg, secondary to keg and so on (it's a general practice not exclusive to, "is secondary necessary" concern - although it sounds like that's what you're asking).
It's one of those procedures in brewing that you may as well try yourself, see if it suits your style and what you're going for in end product. A simple plastic cane is only a few dollars and vinyl hose, not much more. If you do see benefit, you can upgrade to a SS cane down the track but plastic will be fine.
If it is your intention to rack for secondary purposes, or rack to bright (conditioning vessel), it helps to CC before transfer putting your yeast to sleep on the bottom (in trub) allowing for cleaner transfer, where again, you'll be pulling from the top not dumping from a valve in or near trub.
You'll see Pumpy filters his beer, which does indeed negate the need to CC before transfer to keg or rack from top.
reVox