The units that would take most advantage of this would be the Immortal and the Archon. Lets say the upgrade would give 10% more shield life. That would give the Immortal the chance to shrug off 1(if fully upgraded up to 3) extra big attack, but still keep it vulnerable from smaller hitting creatures.
The Archon would gain 35 shield per upgrade, or 105 total, which puts its hp at 455(i think right?). Which would increase the viability of this particular unit as I have also read too many threads concerning the uselessness of this unit.
As for buildings well our most important building, the Pylon, would gain 30 shield points, not a big upgrade but still, as the game goes on the importance of this building grows. This could be a great way for us to help protect our key buildings without giving us an huge early game advantage.
But in some cases like the nexus, its shield life would increase by 100 at a time. However, Zerg's Hive have 2500 Health by the time they upgrade it, and Terran's have the ability to not only repair their buildings but also upgrade their Command Center to a Planetary Fortress as well as have separate armor upgrades for their buildings.