No one can mistake this number 1.12345678 BTC. It is as exact as needed, and if you want a buffer, go add the possible transaction fee. When I deal with people, I state all 8 decimal places, just so we have no misunderstanding, even if the least significant digit is zero, unless I am dealing with whole bitcoins.
Dabs you definitely have a point. Here's the problem with units:
* People don't (even though they could) use commas to separate the numbers. This would make 1.12345678 much easier to read: 1.1234,5678 ... or 1.123,456,78
* Notice the "comma" grouping in our number system (arabic) separates every 3 digits: 1,432,235,439. You can read that number out loud because you can "visually" calculate the reading.
* Speaking of "visually" calculating the reading, this is where it becomes important: your average person cannot distinguish any more than a group of 5 items. When you see that 1 pill is on the ground, you calculate this quickly. When you see that 2 keys are on the ground, this is easy for you to mentally put together. When you see 3 lizards on your patio (or 3 bugs), your mind automatically connect with the fact that there are "3".
* Moving forward: if 4 pens are on the table, you can tell "at a glance" that there are 4 pens at the table. This is an important point, because when you group things by 4 or less, it reduces the possibility of human error.
Given these points above, the reason our number system separates numbers by commas is
not accidental. You might be a super genius that can determine, at a glance, that an entire bag of M&M candies spilled onto the ground is 524 items, but the reality is your common person cannot do that. And that is what using "bits" is all about: for the common person to use with minimal error, and to understand.
My company is constantly dealing with and analyzing bitcoin transactional amounts. At the moment we're using Armory for business operations. And I'll say...it's a pain in the butt verifying numbers, but as long as we use our fingers to help us compare the accuracy of 0.43343433 being created for a transaction and that same amount listed on a spread sheet or contract, we're fine. It still leaves room for error, because after all we're human...
So to reply to your comment, while no one can mistake 1.12345678, there are surely many people who haven't memorized how many digits are past the decimal point--and cannot know at a glance! And there are many variations of numbers within the digits that many, many common people (even exceptionally talented minds) will and have mistaken.