Armor will increase certain protective stats and decrease certain stats related to mobility or flexibility. You'll just have to try it on to see exactly what effect it has. The more protective an armor is the more it will decrease stats related to mobility and/or flexibility.
You should try to have balanced armor to go with your build. Don't lower a stat to much that might be needed or raise one to much that you already have a lot of. If you can find the right balance of Armor and Base Stats you can have a rock hard defense and a steady offense!