First, safer computing is always advised. So, a case to carry big mobile device like phablets helps. Given, proper netiquette to use protection in principle.
Case Netiquette Phablets
In any event, cases protect from drops. Also, water drips. On top of that dirt. Also, snow, just to name a few things.
In extreme weather a good case can save your life if you need to call for help. Dropping is easier than dropping a smartphone because of their size.
A Phablet is as big as your hand while a smartphone is smaller. Dropping a Phablet can crackt he screen and cause other damage. Cases pad the fall and protect the screen from cracks with a cover.
Liquid can ruin a Phablet because they are digital and digital devices short circuit when they get water in them. Therefore, it is good netiquette to use a case to protect Phablets because a good case can prevent damage from drops, cracked screens, and water.
Case to Carry Netiquette
Put it in a case because large screens are easy to crack.