Is defraging bad for my computer?

While running various features of my Norton software I noticed that it was automatically carrying out a Hard Disk 'optimisation' ---- in other words defraging the Hard Drive.  Now, it is my understanding, having been advised from more than one source, that this defragging is bad for my Hard Drive, that it shortens its life and should not be done!.  I cancelled it . My HD in my W8.1 Tablet is, I believe, an SSD which I take to mean a Solid State Drive, which should not be defragged. 

First, can this be confirmed and secondly can anyone advise if / how I can set Norton 360 to not optomise / defrag?

Clayto