I left my bike in PDX a few days ago, won't be back for 4 weeks (7/4,5 and 6 at The Ridge). I forgot to loosen the front straps (back of Tacoma) and the forks are slightly compressed.
I'd assume that depends on the level of compression. It could definitely cause permanent damage but again, depends how far they're compressed. Doesn't sound like a good idea to me.