The first point in this perk is vital. If you want to ever be able to sneak anywhere at all, you need to invest a point here. Ranks 2-5 of this perk are all less effective and less important by a drastic degree, and each rank further becomes less important than the rank before it- but pretty much everyone wants one rank of this. Find a spot to spare a point for the perk.
A basic thing for anyone who wants to play a skulker and a rogue, you want this perk if you plan on starting combat while hidden. Even if you don’t plan on using single-handed weapons in such situations, in fact, since it’s required for a perk that every single sniper wants- as do many other archers. If you do plan on striking from the shadows in melee, the damage this enables is hilarious- it pretty much guarantees that the first thing you smack in the combat is going to start the fight dead.
This is the start of the side of the Stealth perk tree that is mostly of questionable value. While it’s very useful early on, the effect of this perk gradually becomes outweighed by the availability of stealth-enhancing spells and enchantments that will give you a better effect without permanently consuming a perk point. Consider the entire branch of the tree carefully before choosing to get this perk or not.
The main reason that everyone wants to consider taking Backstab, this can make archery before the start of a fight incredibly vital. Snipers, who already boosted the everliving daylights out of their archery damage via Archery tree perks, will find the damage boost immense, turning sneak attacks from x2 into x3 multipliers to their already swollen shot damage. Warriors and the like will benefit hugely from the increased chance of crippling or outright eliminating an enemy from an upcoming combat. Rogueish sneaky types, on the other hand, don’t care. They’re far more interested in getting the x6 bonus from sneaking into melee range with an axe and lopping someone’s head off. Mages, meanwhile, couldn’t give a fistful of sawdust about this.