A visitor log is the oldest artefact in this category and the one every reception already has, usually as a hardback book with a pen on a string. The electronic version holds the same four facts, and its whole advantage is that they can be found again: who arrived, who they came to see, when they arrived and when they left. Everything a visitor system sells is built on that record.
The four facts, and the one that is always missing
Name, host, in, out. The last one is missing from almost every paper book, because signing out requires the visitor to walk back to the desk and remember to. An electronic log makes the gap visible, which is uncomfortable and useful: at least you know the list of who is inside is wrong, and can do something about it with a badge prompt or an end-of-day sweep.
Keeping it is a decision, not a default
A record with no retention period grows forever and nobody deletes anything, which is how a reception ends up holding several years of personal data with no reason to. Pick a period, write it into the policy, set the product to enforce it. Under California's privacy law and its equivalents elsewhere, the ability to say what you hold and for how long is a basic expectation, and a log that grows without limit cannot answer either question.
What people actually ask a log later
Was this contractor here on the fourteenth. How many visits did that firm make last quarter. Who was on site when the alarm went. Who signed in during the two hours the server room was open. A book answers all of those with somebody leafing through it, which means in practice nobody asks. A searchable log turns them into a filter, and only then do people discover they had questions.
The book still has one advantage
It works in a power cut. Keep a printed sheet in a drawer for the day the network is down, use it, and type the entries in afterwards. Sites that skip this discover the gap in their record months later, when it is the only thing anyone wants to look at.
Questions people ask about electronic visitor log
How long should a visitor log be kept?
It is your decision and should be written down. Long enough to answer a question about an incident, short enough that you are not holding personal data with no purpose.
Is an electronic log admissible or evidential?
It is a business record like any other. What makes it useful is that it is complete and timestamped by the system rather than by handwriting; what makes it weak is missing sign-outs.
Can visitors see who else signed in?
They should not. A paper book shows every previous visitor to everyone who signs; that alone is a reason plenty of sites move off paper.