Did we not have this exact thread about 2 weeks ago?
Where a new line damages an existing line, I’ll often trash it. Where the 2 can coexist, I leave it. Also consideration of safety/visibility (ie, whatever fanny it was that built the jump that went straight onto a popular walking path near my house
I’ve mentioned this before but of the organised trailbuilding sessions I’ve done recently, at least half of our time was spent blocking off damaging shortcuts. None were remotely interesting, they were all about avoiding corners. We did leave a couple in place as they weren’t causing a problem and added an interesting option but that’s a rarity. And the effort people put into clearing them once blocked is amazing! We’re not talking about just riding off the line, but moving cubic metres of brash, decent sized trunks, etc.
To be fair, armoured trails are a bit different, as shortcuts cause
permanent damage to the armoured surface.