This line applies your global_policy policy-map to all active interfaces on your ASA. So, any traffic that comes in on any interface will be subject to the inspection rules defined by your global_policy (assuming it matches a class-map).
Without seeing the rest of your configuration, it is impossible to say how removing this line will affect your firewall. Take a look at the output of 'show run' (or 'show run | b class-map) and 'show service-policy' to see the inspection rules that are applied to this policy.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...