The bandwidth limit feature is very handy for when one has a slow speed WAN connection.
I have a router with a full-time slow ADSL WAN connection and a hot-spot based fast connection (5G) that's not always available.
It's annoying to have to turn off bandwidth limit when wanting to use the performance of the 5G connection, but essential to have it to avoid large uploads disrupting normal usage.
It would be much better if bandwidth limit could be applied per WAN interface.