Its not necessary for multihoming. I am el-cheapo multihomed using Linux router. I use policy routing with 2 default routes (primary and secondary) and everything works like a charm. I could even try to do some ECMP but I care more about stability of ping/jitter that raw bandwidth. And you dont need to bother to ask ISP for BGP or static IPs. You just take whatever you have and slap it together.

Yes, which is why I said useful. With a full table from two ISPs you know which ISP have a shorter path to a CIDR. It's also likely the same path where traffic also comes in from that CIDR.