It is quite common for users to rely on videos when they want to create a demonstration or illustrate a situation: they record the desktop activity, then save it as a video.
Joining these clips occurs when there are multiple videos and they need to be exported as one file.
FLV joiners will also allow users to merge several shorter videos and create a single large item.
Some of these applications will offer users the possibility to adjust the source files' sample rate or resolution before joining them.