Some videos are worth keeping because you know you'll watch them again. A tutorial you need for work, a lecture before an exam, or a playlist for a long flight can all be easier to access when they're available offline. That's one reason many people look for a YouTube downloader that lets them save content for offline viewing.
Another reason is convenience. Internet connections aren't always...
SkillClick
English
Arabic
French
Spanish
Deutsch
Turkish
Dutch
Italiano
Russian
Romaian
Portuguese (Brazil)
Greek