Tents are a big nuisance for me, but haven't done much other than set back growth rates with their appetites. If I was counting on inches per year from my trees, they'd be a big problem. Since I'm along for the ride rather than a serious timber investor, I'm more upset with their poop slime falling from the sky than the leaves they've devoured creating it.
If I was suffering mortality, things would be different. Their poop slime is nasty none the less.