This topic is almost like asking a) how often do you change oil? and b) what kind of oil you use? There’s what the manual tells you to do, and there’s what people actually do, and some of it is very surprising. One the one end of the extreme, you have people changing oil every 500 miles, when the manual says 3k miles. On the the other end of the extreme, you have people who says it’s fine to change oil every 7k miles or more if you use synthetic, and they have oil analysis data to back that up. For chain lube, the common recommendation is every 500-600 miles, but like TrialsRider pointed out, there are many high mileage riders, including adventure riders who do a lot of dirt, who say they hardly ever clean sealed chains (o-ring and/or x-ring), lube infrequently, yet their chains still last a long time. There are those who say WD40 eats o-ring seal, and others who say they use nothing but WD40 on their o-ring chains. One time I asked a trusted bike mechanic (from the UK where it rains a lot) if I needed to lube the chain much more often during the winter rainy seasons, and he surprised me by replying that you might do it a bit more (like lubing every 3-400 miles instead of the normal 5-600 miles) but not a hell a lot more.
Personally, I feel the manuals’ recommendations are conservative for normal use, so I tend to stretch my oil change and chain lube intervals.