ELC: Using LTTng

I'd say that LTT is more for looking at what happens in the whole system (from the kernel point of view), especially when you don't have any idea about what could be reason for the issue you're investigating whereas ftrace is more for looking at some specific area within the kernel, when you either already have some idea about the (potential) cause for the issue or are only interested about a specific kernel area (like say a file system maintainer would).

LTTv being able to easily process gigabyte sized trace data and to view it interactively helps a lot.