I spent the week using Find Identical and Union over and over across several projects.
Both of them have settings that I always want to use, but are not the default setting.
For Find Identical, it's "Output only duplicated records".

For Union, it's "Attributes to Join --> All attributes except feature IDs"

Having used both of these tools something like 80 times each this week, I would really prefer to have the option to save certain parameter values as a user-specific default. I think this would be good for any choice value list or boolean parameter. For example, the option to save "Geodesic" as the method in the buffer tool

Or perhaps being able to set a default unit to use in the buffer tool.
This has been a pebble in my shoe for the last week. I recognize that not everyone has the same needs or preferences as I do, but I'm sure they'd like being able to save their own preferences.