A SharePoint public/cumulative update includes security fixes for the product as well as it may contain fixes for the problems reported through MSFT support.

 

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Usually security fixes & functional fixes are released as a separate package on a monthly basis. We must install both the packages together as it is the MSFT
guideline.

Microsoft recommends that all customers install Public/cumulative updates for SharePoint Server 2016 as soon as they become available. Microsoft performs rigorous
validation of each Public Update, both internally and with a select set of partners and customers before it is released to ensure it has the highest quality.

Updates are cumulative, that’s mean include all previous updates, so if we miss the last 3 updates and want to install latest then it will cover all.

Official recommendation is install updates ASAP when they available. But, I would validate the update in my Dev/UAT environment before taking it into Production.