Preventing blacks and poors from voting of course.
The US is one of the few western democracies that doesn't have same day registration.
IL has same day registration and there are still paper books of voters for each polling place. It didn't eliminate the need for judges to check people off the paper list and record that they had voted. Many of those precincts include electronic poll books, but there is still a paper backup.
Does every other western democracy now have tablets or the equivalent in every polling place to record voters as they come in? The only foreign election I've observed was in Germany in 2002 and everything was on paper then.