During times of great conflict, Jedi would sometimes require the use of battle armor. Armor-clad Jedi were a common sight on the battlefields of the New Sith Wars, while the ancient Jedi of the era of the Old Sith Wars would often wear parts of armor to protect certain areas of their bodies, as would many Jedi of the New Sith Wars era. Shoulder guards were especially common among the ranks of the ancient Jedi.
Jedi armor was designed to be light and comfortable, giving the wearer as much freedom of movement as possible. However, the freedoms provided by Jedi armor were very limited compared to those provided by traditional Jedi robes. In the ancient wars between the Jedi and the Sith, the battlefields were often so packed with combatants that moving about freely on the battlefield would be difficult even without armor. This would result in immobile and poorly protected combatants, which may be why the Jedi of those eras chose to prioritize armor to mobility.
Finding particular use in the Army of Light under Lord Hoth during the New Sith Wars, Jedi armor was designed to be comfortable for the wearer, light and give the wearer the ability to use the Force as much as possible.