Start and end clips are a part of your brand's video-identity.
Start clip is the introduction to your video, where you can display your brand's logo, tag line and other things that make you unique.
End clip comes at the end of your video. Here you can display your logo, website address, social media links, messages like "stay tuned for more."
These clips are your unique way to say "Hello" and "Goodbye" to your viewers.