Not wanting to sound patronising, you should verify your understand of NAT;
Clients on the LAN likely have a private IP addresses (from RFC1918) that are not routable across the Internet. The two WAN interfaces likely have public routable IP addresses allocated from the two ISPs they are connected too.
When a host on the LAN connects to a host on the Internet such as a web server, it makes the request to the ASA, and the ASA passes on the request to the remote Internet host but translates the IP address of the LAN host within the request, to one of its public IP addresses. If the ASA sends the request via the first WAN interface the ASA will change the source IP of the request to the IP assigned of the first WAN interface;
Action Translated Packet:
If the request is sent via the second WAN interface it uses the other rule,
Outside-ISP2 and the request is modified to use the source IP of the second WAN interface, instead of the LANs internal private IP address.
If you drop either of these NAT rules, the LAN host addresses aren't translated into a public routable address and the request sent to the website and will not be answered, because the website can't communicate back to a host on a private IP address, it won't know where it is or how to get there across the Internet.
As both the rules are seemingly the same, just looking at the first one:
SourceInt DesInt Source Destination Service Source Destination Service
3 inside Outside-ISP1 obj_Any any any Outside-ISP1 original original
This rule is saysing "Any traffic that comes into the interface called
inside (which is likely going to be the LAN interface), which is destined for the interface called
Outside-ISP1 (which is likely going to be the 1st WAN interface, also it will be going there probably because of a default route on the ASA), that comes from the source IP matching those in
obj_Any (which likely matches any inside LAN host IP) looking to reach a
any and through a
any; Will have it's source IP changed to
Outside-ISP1 (the IP of the WAN1 interface) and the
Destination left as is, and the
Service left as is.
These extra option for matching traffic based on destination and service, can be used for other kinds of NAT rules such as port redirection or policy based routing.