What is pros if i set forward port

[klo123645]

this is my system diagram

my plc read data from remote i/o
i use RUT956_2 as repeater
network 192.168.1.0/24 no issue but network 192.168.4.0/24 can not reach
when plc read remote i/o 192.168.4.100:502 will access via 192.168.10.120 port 502

question

1. what is a pros of this diargram
2. have a another method to access network 192.168.4.0/24 from PLC