To be specific, I am talking about the link below from the 3.x NI License Manager (this is on a VM I use for LV 8.5 development)
It had the nice feature of filling in your computer's information and all the products you are activating as part of the link. Unfortunately, NI's website no longer supports this pre-filling - using this link in 3.x now just redirects you to the normal result of typing in ni.com/activate into your browser.
My typical workflow with this screen would be to enter my real serial number into the preceding dialog, use this dialog to get the activation link, go back to the preceding dialog and enter in a fake serial number, press next twice to get the activation codes entry dialog, and copy the activation codes into the dialog.
In NI License Manager 4.x, you either need to use web activation (which saves your serial number everywhere) or enter codes manually, requiring a trip to http://ni.com/activate for every product that needs activation (and trying to figure out how the name of an application in License Manager - say "Vision Development Module Runtime" - matches against the website's entries - say "Vision Development Module", "Vision Development Module (FRC)", "Vision Development Module Runtime (FRC)", and "Vision Runtime") and a bunch of e-mail spam if you choose to get a copy of the activation e-mailed to you. Note that activating LabVIEW alone requires two of these trips (or at least used to), as the Professional Development system and the Application Builder activate separately.
As far as why I often don't want to use the built-in Web Activation, it stores your serial number on the computer. This leads most (I think LabVIEW 2017 is an exception) versions of LabVIEW to display your serial number in their splash screens and about boxes - this could be visible in a public setting or at a customer site. It also stores the serial number even after you deactivate it, so if you temporarily activate a tester while you are doing its initial debug, your serial number will be stored for your customer to reactivate (and possibly distribute).
I labelled this as MAX, as there is no License Manager Idea Exchange - in a way this applies to all NI products.