This iOS feature is very handy in a day-to-day life. You can customise Vibration pattern for various alerts so you know without looking at your phone what type of alert it is or even who sent it. (Like a Phone call, Text message, Voicemail, etc.)
Try it out by yourself using following steps.
1) Open “Settings” and tap on “Sounds”
2) Scroll down to a section where is says “Sounds and Vibration Patterns”
3) Select the Alert type you’d like to change (Ringtone, Text Tone, New…