How to customize LR develop default settings to save time?

Camera processing defaults are great, user customised as necessary, for specific processing which addresses how one camera differs from another as to its baseline appearance. What level of NR or camera calibration profile etc you prefer to see, with a Nikon XYZ camera at 800 ISO.

However before choosing to implement such "general preferred defaults" as post-crop vignetting by updating the processing default, it's a good idea to consider:

• applying an updated processing default onto a previously edited photo, is unselective : your only option is to Reset that photo completely, and this obliterates ALL work done to that photo since import, by the user
• a preset can encapsulate only selected settings, so when applied (at import) or reapplied (later), it updates only those particular settings while leaving the image otherwise alone.

Also

• different processing defaults are maintained, and updated, per camera model
• for each camera model, you furthermore have separate processing defaults for Raw and for non-Raw
• for each camera model / Raw or non-Raw, you may have further separate processing defaults for different ISO settings, if you have configured LR to do this - and/or, for the same thing for different camera body serial numbers

Hence you may have many different sets of processing defaults to separately update in this same respect. That's laborious.

So IMO a develop preset (with a selective scope) is by far the better way to apply that kind of thing. At import, or subsequently. You only need ONE such preset, to make and later to update as needed - and you can then apply or re-apply this single preset onto Raw or non-Raw photos taken by any camera model at any ISO etc. Without losing the remainder of your pre-existing edits, nor overwriting any other default processing which a particular image may happen to be showing because it was taken with a Nikon XYZ, in Raw, at ISO 800.