It not as effective as shield especially if you have elemental block perk, but for magic user enemy especially dragon they are very effective.
You just have to train how to time your wards with enemy attack.
Also they are kind cooler than shield
It is very useful against magical attacks, but almost negligible against physical weapons. A few of the restoration perks are needed to be able to cast it for any length of time, otherwise it eats through magicka at an alarming rate.
I must say though, they are almost required for my character when facing a dragon.
Wards are useless for my mystic archer. She needs both hands for her bow. So, she focuses on pushing resist magic up instead and likes that better because it is passive and leaves both hands free for a bow. With the max (85%) magic resistance, she can stand at range vs a dragon, shooting arrows into his fire or ice shouts. She'll survive; the dragon will not. Her big vulneraility is vs melee - and a ward not only completely eliminates her bow offense but, as King Coin said above, doesn't help that much vs melee.
On the other hand, she likes it very much when an enemy mage brings up a ward - for three reasons:
1. It is fairly useless against her arrows.
2. It means the mage has one hand occupied doing something that can't hurt my character.
3. The ward makes a great target to make hitting the mage with a bow easier.
never used them, the best way to win a fight is from so far away your arrows need a map to find their mark. not running around using magic and getting mauled to death by a bear when you run out of magica. seriously who named it that?
the only use I had in wards was to pass the entry lv exam to becoming the archmage. Aside from that, never use em.