Except you do lose out on best path routing / any other outbound TE, and you’re now restricted to rudimentary load balancing methodologies / manual prefix-specific hackery.
For a home network I'm guessing you are pretty unlikely to do the multi-homing from the house, more likely you will either just have a single upstream or if you are connecting it into your own collocated infrastructure you will do iBGP and let your actual edge BGP routers handle the multi-homed upstreams and sync the full route table etc.
I was tempted to do this once before when I was running my own hosting company but it was prohibitive cost wise to get the circuit I wanted. :(
The parent I was responding to was explicitly claiming no downside to being default-only while multihomed.
Noction is a wonderful example of this. It has sane defaults, but insane customers, who think that it’s a good idea for them to originate more specifics for other outside networks, because they’ll never leak them outside of their own AS (narrator: of course, the prefixes leaked).
I think the most notable example of this recently was Verizon (the insane customer) using Noction (the SD-WAN technology) and doing exactly that, causing mass traffic disruption as they announced more specifics for other peoples prefixes, drawing all that traffic to their own network instead.
After 3-4 hops you're probably hitting a Tier 1 network, after which point you can basically think of the Internet like cloud icon you see in many diagrams, because your route choices are no longer really determining reachability, rather the choices of other people/companies are:
* https://en.wikipedia.org/wiki/Tier_1_network
If you're talking about reachability of a network on another continent or the other side of the planet, your local decisions aren't going to much to determine the path.
The main thing to have locally for routing decisions is the ASNs/networks of the other customers of your ISPs: if Service A is also a customer of ISP #1, you want to send traffic for them through that service instead of ISP #2.
The other nice thing to have is the reachability to the closest IXP, as quite often many CDNs have connections to those.
Beyond knowing IXP reachability and other-customers reachability, I don't think there are many other advantages for a smaller entity on the Internet, so a full Internet-wide BGP is not needed.
For eyeball networks and other stub networks this is mostly fine.