Illusions have had many uses, mostly trickery and entertainment. One
more practical use is to cast a spell on a target which bends rays of
light around them, causing anyone who can see them, to see a slightly
distorted image. This causes any physical attacks to be somewhat
mis-aimed, since they are not based upon the true position of the target.
While it far from guarantees complete protection from physical attacks,
every little bit helps.
Blurred image is available in the following guild: