I have been a poll watcher three times, in 2008, 2012, and 2016. These comments are based on my personal observations. Voting is a right of all citizens, but sometimes we provide roadblocks to voting. The first two times I was a poll-watcher were in Eastern Jackson County, Missouri, the last in Indian River County, Florida.
In 2008, I was a poll watcher in Blue Springs, MO in Eastern Jackson County. Blue Springs is not adjacent to Kansas City, so I do not recall issues of Kansas City voters moving to Blue Springs, or vice versa, so there was not confusion between the Easter Jackson County and Kansas election boards. A voter can move within Kansas City (Jackson County) and change addresses on voting day and still vote. Likewise when voters move from one eastern Jackson County location to another. The problem arises when a voter in Jackson County moves to or from Kansas City to or from Eastern Jackson County. Even though the move is within the same County, if the voter does not report the address change in advance (I think 10 days) he or she is disenfranchised.
The scenario above, moving to or from Kansas City to or from Eastern Jackson County became a real problem during my second assignment in 2012 in Grandview, MO. Kansas City and Grandview are adjacent cities, and voters regularly moved between the two. If a Grandview voter moves to Lees Summit without changing his or her address, the voter is okay, since both cities are in Eastern Jack. But, if that voter moves to Grandview from Kansas City, without changing addresses formally, even if the move is a couple days before the election, the voter cannot vote, even though the voter is still within Jackson County. The voters I saw who were turned away from the polls were primarily African-American. I think the 10 day rule for changes of addresses with the same County, between Kansas City and Easter Jack, is probably unconstitutional. It deprives citizens from the right to vote.
What I witnessed in Florida was much worse. In Florida, if a voter has not voted in the last two elections, he or she is removed from the polls. The voters have registered, have not moved, but just decided they did not want to vote, and bam, they can not vote in the subsequent election. I suspect this rule in Florida affected Trump voters more than Clinton voters, because, presumably those who had not voted in the two previous elections chose not to vote for Obama.
In Florida, there is a voter i.d. law similar to the one just passed by the Missouri electorate. Voters must have an official photo, drivers license, passport, etc. to vote. This caused much frustration. Many elderly voters had no official identification. The other voters with no were overwhelmingly African-American. Voting is not dependent on us having a level of sophistication whereby we each must have a car or hope to travel internationally, and the ability to obtain state identification for poor people without restriction is limited. None other the turned away voters seemed like their intention was to commit voter fraud, since voter fraud is a rare thing. Many of those turned away from the polls will probably never vote. Being turned away from voting, exercising a citizens' right, can be humiliating. I suspect that was the first and last attempt to vote for many U.S. citizens.
Some states allow voter registration up to election day, early voting, and even voting by mail. Some states encourage their citizens to vote. It's sad that even the ability to vote has become partisan.