Shadow Blade is an agile item for most of the heroes with sneaking and bursting damage abilities. This item is very suitable on heroes such as Drow Ranger, Faceless Void, Slark and many more. Shadow Blade can also be used for initators, but this varies on the opponent whether they have detection items such as Sentry Wards or Gem to know your presence even during invisibility.
Shadow Blade is a great item for moving through the map or mobility. Even though there are wards being planted on certain places, some of them did not put sentry wards. With Shadow Blade activated, you can walk through all those places and sneak attack on your enemies without a doubt.
In other words, Shadow Blade is also known to "bully newbies" because most of them will not get a detection item. From this you can do lots of "hit-and-run" kills which will cause your enemies to be scared to go out to get some farm or even farming in the jungle.