What good ideas, StanleysChesterton!
I tend to include in-laws / married ins, because as you say, they can help you find odd people here and there.
I'd like something that showed adoptions, especially where the true parent is known, and I'd love a button that eliminated any hint NOT in England!
Also "unknown relative" might be nice....
Also like a "floreat" box, when one's not sure about birth or death but has documents showing existence at that time...
Save a lot of time browsing about in idle moments ... but then: what would one do with the time saved?
Seriously, I also use paper and a "Main tree" - and branch trees in both directions are on other sheets, for cross reference when needed