disable mod_security = dangerous?

I have had many issues with this blocking out certain words (btw can anyone explain why this happens? it was driving me to complete madness until I figured it must be this).

My host tells me they highly recommend against disabling mod_security though, as it then poses some large security risk.

Can anyone expand on this please? I have databases with peoples names/phone numbers/addresses/ etc stored on them, i dont want to open up any security holes

Thanks