Absolutely, but you're reducing the risk of communicating with people who may be using the roman suffix without writing in Roman numerals. In that situation, you'd see 2M rather than MM.
The British billion went out in 1974/5 (Wilson/Healy). One billion is 1,000,000,000 and you shouldn't expect ambiguity there.
In practical terms, it doesn't matter. It'd be extremely unusual to be at the scale of the old billion (1,000,000,000,000)
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This is similar to a justification of using `i` as the variable for an iterator, or `x` and `xs` for head & tail. There are logical reasons, but it's mostly convention.
Thanks for the explanation though. Next we'll get into how a european billion is 1000 times more than a US billion.