I do a uoa on my cars (this will probably be my only one) to make sure there are no problems,obviously because they are used cars and you never know how they were treated or why they were traded/sold.
Sure,a 3/3 oci on $20 a quart Eneos would be silly,but on $18 per 5 quart jug Quaker State,no comparison. If an initial uoa showed crazy wear metals,that car would get unloaded asap.
I also change brake fluid/power steering fluid every few months,transmission fluid once a year,and coolant once a year.
I'm very ocd with my vehicles because I have to count on these vehicles impeccably to never let me down.
Then you have the ones who think all oil/cars can go almost indefinitely without change or maintenance and wonder why their engines suddenly seize up or fall to pieces.