That's a nice feature... when it works. You really need to be careful when buying by the complete series. Here's one really quirky example - let's say you want to buy all the Punisher MAX volumes. Amazon has this for the full series:

https://www.amazon.com/dp/B07JKH936M

Vol. 7 is conspicuously missing from this list. In fact, it's in its own "series" of books here by itself:

https://www.amazon.com/dp/B07JK6C3NM

On top of that, the first link above has both Vol. 6 and Punisher: Frank Castle MAX - Welcome to the Bayou in it. The latter collection is made up of Punisher MAX #71-74, which is included in Vol. 6! Buy the entire "series," and you've just wasted some of your money on a duplicated collection, and potentially missed out on the final volume (though to be fair, Vol. 7 collects a subsequent Punisher MAX series).