I tend to phone to ask for any extra info, but I must be honest and say I don't get the objections to doing it, but I think if you want to just jump in then that's also fine.
I'm not some airline wanna-be all up on Pomp and Circumstance and procedures and would love to see a Transport System made out of GA where you can somewhat jump in and go 24/7, but if you want to spend 100GBP per hour or whatever flying somewhere only to find out that you can't land for some stupid reason - then I would have preferred to have known this before I set off so that I could decide on another plan.
It's only so that the £200 quid bacon buttie doesn't cost me £400!!!