900 mhz external filters?

What are the 900 mhz filters for? Yes, I know, you’ll probably go duh!!!, but, really. Would it be good to install them from the start or what would you use them for if interference is outside the band? Also, Should I be using the external filter delay setting on the AP? The manual says to ignore it

We used external filters from Last Mile Gear for a while but removed them on some APs due to the insertion loss of a dB or two. The few dB decrease in signal caused problems for a few fringe customers. But, this weekend I will be climbing two towers to install the filters again on different APs because the fringe customers are having problems anyways. Turning the AP into an SM and enabling the SA showed huge amounts of signle in and around the 902-928 band. These filters are sharp enough to cut out the cellular (down low) and paging (930+) out and hopefully will stop the unwanted signals from hammering the rx. Hopefully this will cure the problem of a few of our subscribers from dropping intermittently.