Payment batching, as illustrated with calculations from Optech's tx calc, showcases significant savings in transaction sizes. Without batching, three transactions, each having one input and two outputs, accumulate to 462 vbytes. When batching is applied, the worst-case scenario shows a reduction to 355 vbytes, saving 23%, and the best-case scenario drops further to 240 vbytes, reflecting a 48% saving.

The conversation then shifts towards the additional efficiency gains possible with CISA alongside batching. Two scenarios are presented: half-aggregation and full aggregation. Half-aggregation reduces the size of subsequent inputs by 8 vbytes each, leading to a total size of 339 vbytes, or a 3.6% additional saving from the non-CISA batched case. Full aggregation further diminishes each additional input size by 16 vbytes, bringing the size down to 323 vbytes, which translates into a 7.1% extra saving. This analysis underscores that while CISA enhances the efficiency of batching, the improvement is relatively modest.

Furthermore, the argument posits that concerns regarding CISA as a privacy issue are unfounded. The introduction of CISA is not expected to necessitate a new address format, but even if it does, such a format would likely support a wide range of output uses, akin to Taproot, eventually becoming the standard. The transitional period, where upgraded and non-upgraded wallets might be distinguishable, should not deter the addition of useful features to Bitcoin.

Lastly, the email touches upon the broader implications of CISA beyond mere transaction efficiency. It points out that CISA could lower the costs associated with creating coinjoins and payjoins, privacy-enhancing protocols already in use. Moreover, the potential for CISA to reduce the cost of other current and proposed privacy-centric protocols is acknowledged. Even though the cost reduction might be modest, any enhancement to privacy is deemed worthy of consideration, signaling an overall positive stance towards both batching and the introduction of CISA in the Bitcoin ecosystem.