It is too easy to punch in numbers and blindly accept the electronic answer. Unfortunately, if the numbers or decimal points are entered incorrectly, the answer will obviously be incorrect. If the user has no concept of approximation and what the answer should be, they will continue on, with totally useless and in some cases devastating results.
A case in point being the $125 million Mars orbiter which crashed in 1999 due to a mix up in units between imperial and metric.
If the Engineers had been forced to look at the data and THINK, then very likely the alarm bells would have been ringing immediately, that something didn't add up.

Whilst the slide rule is not accurate to ever increasing decimal places, it doesn't matter. How many times do we need an answer to 10 decimal places ? It's a gross overkill which just causes confusion.
Apply the KISS principle and Keep It Simple, Stupid.