FC protects the porous western border. Since our independence we didn't keep any form of force on our western border keeping the border insecure and porous. Our focus was always the western side. However the situation was changed and we require a border control force which is the FC. Noe the FC is supposed to be the paramilitary force that keeps the peace as well as are respondents on terror attacks as well as protect the border. This is a huge burden on an 80000 force.
Plus the border of afpak is 2250km with many points mountain ranges which cannot be fenced or trenched. We may have trenched the 1100 km border of Baluchistan but the border of kpk and FATA is not easy.
So to combat this we need check posts at many sectors to combat infiltration. It may never end ( these afghans will scale the great wall of China ) but it can surely be reduced and considering the situation in Afghanistan it become imperative that more and more check posts are raised. To man those check posts and to secure the border we need to have a well equipped and well manned border control frontier corps. The border cannot be allowed to be kept porous.
Remember the threat from the western and eastern are different in nature.
The western border threat is terror infiltrators and illegal immigrants. The terror infiltrators will require posts to keep an eye on this form of movement.
The eastern border threat are invasive in nature as larger armies coming with armoured corps and air force so it requires more technological defensive force aka Sam system, anti tank systems as well as a defensive collective capability.
The govt and the army are currently increasing the number of FC so the demand is being met on the behest of strategists and analysts in our military force.
https://www.google.com.pk/amp/tribune.com.pk/story/967411/massive-recruitment-leas-strength-raised-by-27-in-balochistan-over-4-years/?amp=1?client=ms-unknown
There was another news piece a few months ago where nisar said that FC will raise few more divisions. I can't find it but I made a thread here about it.