`createTRPCProxyClient` vs `createServerSideHelpers`

I see T3 app router is using

createTRPCProxyClient

createTRPCProxyClient

for server-side helper, why? what is the difference between it and

createServerSideHelpers

createServerSideHelpers

. I'm using

createServerSideHelpers

createServerSideHelpers

right now so i was confused. According to

trpc

trpc

's documentation, shouldn't we use

createServerSideHelpers

createServerSideHelpers

instead since the client and the server are in the same app?