I'm not familiar with Netscaler, so take this with grain of salt.
I presume you are using NAT to translate source address of request today, so actual server is not seeing today real request address but some single NAT address translated by Netscaler.
I also presume that his toggle would remove that source address NAT, allowing your servers to see real request address.
There are some scenarios where one would want to NAT the request address, such as if for redundancy purposes you want to connect your server to two or more SLB devices simultaneously (who would ECMP the VIP, i.e. both SLB are hot:hot, but not connected to each other in anyway). Then when your server replies to a request, it needs to reply via same interface where the original query came in from.
On Linux machines you can fix this easily, without relying on natting the source at SLB.
On Windows server, you wouldn't really have any way to return the request back to the SLB which sent it, unless you NAT each request. If SLB1 NATs source to 192.0.2.1 and SLB2 NATs source to 192.0.2.2, then it's just matter of setting static route in windows, 192.0.2.1/32 pointing to SLB1 and 192.0.2.2/32 pointing to SLB2. This way you are always returning packet back to the SLB which sent the request.