Ingress VLAN translation rules are for PVID (Port VLAN ID) configuration. PVID is a default VLAN id assigned to frames coming to the port. PVID is required on Access ports where usually PCs and other end-user devices are connected.
Egress VLAN Tag table contains configuration for VLAN Trunk ports - ports which forward tagged frames to other VLAN aware devices.
In short, proper VLAN configuration on CRS switches:
/interface ethernet switch ingress-vlan-translation
/interface ethernet switch egress-vlan-tag
Egress VLAN translation rules is additional option to modify VLAN header once more before sending out packet from the CRS port. They are not necessary in basic setups.
Real world application examples with CRS switch are described in wiki manual: