According to [benchmarks](https://github.com/ethereum/builder-specs/issues/53) related to encoding and decoding of signed-blinded-beacon-block payloads with SSZ vs JSON

> SSZ seems 40-50x faster
> Considering 20-40ms per coding on average, that's up to 200-300ms JSON latency (or more).
>
> Sending the data SSZ encoded could reliably shave 200-250ms off each getPayload roundtrip.

Recently I've worked to support SSZ request bodies in lighthouse in `POST beacon/blocks` and `POST beacon/blinded_blocks` endpoints via the PRs below:

- [Support SSZ request body for POST /beacon/blinded_blocks endpoints (v1 & v2)](https://github.com/sigp/lighthouse/pull/4504)
- [add ssz support in request body for /beacon/blocks endpoints (v1 & v2)](https://github.com/sigp/lighthouse/pull/4479)

To support the block proposal flow using SSZ end-to-end, I have added SSZ support to the following block production endpoints:

- `GET /eth/v2/validator/blocks/{slot}`
- `GET /eth/v1/validator/blinded_blocks/{slot}`

via this PR [Add SSZ support to validator block production endpoints ](https://github.com/sigp/lighthouse/pull/4534)

Per the benchmarks this should be a nice optimization for the block proposal flow.

There is also a related issue to using SSZ in builder API queries: [#3701](https://github.com/sigp/lighthouse/issues/3701)

If/when that is ready to be worked on I will most likely pick that issue up next.