Ice Barrier is a seemingly simple first eraFrostbuilding. While it does not do much on its own, it can be used in a myriad of ways and combos well with many Frost cards. Its only ability is rapid construction, so its construction time is very short relative to typical buildings.
The most obvious use, which is rare, is simply using multiple Ice Barriers as a wall. It won't have as much health as a regular wall, but it
can be used to block off a area from M, L and XL creatures.
One of the uses for Ice Barrier is as a stationary tank to draw enemies away from attacking weak units. Though it may not have a lot of lifepoints, it is very inexpensive (20 power), and unless the attacker has siege, it will not receive damage bonuses that it might against creatures. Since players have little direct control over aggro, this is perhaps a less-used tactic. Alternatively, they can be used to bait and herd enemies into kill zones. Whether enemies attack the barriers or not, they can be drawn in the general vicinity and within range of archers and mages. This is particularly useful with White Rangers' Home Defense ability.
The more common tactic is to enable Frost creatures' abilities that require proximity to friendly structures. Lyrish Knight, Home Soil, and Ice Guardian are just a few examples of creatures that are only fully effective near allied buildings.
Also, your units slowly regenerate Health when they are near any of your own buildings. Ice Barrier can put this to use by acting as a fast way to heal your units that are far away from your base (due to its Rapid Construction Ability and low Power cost).