Thoughts on physical barriers and shields?

[Kriegson]

Just curious as to what people think of engineers potentially placing physical barriers virtually wherever they please, and certain unit types having access to physical shields?

I understand that realistically, ballistic shields are neither particularly effective, nor useful. On the other hand, with exo-suits and various bits of incredible technology and material forging methods, I would think you could create a "modern" shield to deflect bullets the way a medieval steel shield could deflect arrows.
Perhaps used by MAX's or HA's to help better defend or assault bases and other enclosed areas, or fight their way across killing fields.

I'm not really advocating the idea, I've never really seen ballistic shields done well in any shooter. Just curious as to what others may think.