Apart from liberating the space in your bureau taken up by that bulky chequebook and 10xC5 envelopes, what problem would this fix?
having to have envelopes
Having to have paper in the printer, and the printer (which is in another room) switched on
Having to fix the paper jam/go to town to buy more paper/ink/etc (we don't print very much these days)
Having to have stamps (this is a major problem in the Volio Household; we really rarely use them)
Having to write the envelopes [or buy a printer that prints them, and doing the word processing]
Having to find the damn chequebook
Making sure it'll all go in the envelope such that the PO don't charge extra for it
Sticking down the envelope with sellotape because it's not sticky enough
Finding the damn sellotape
Going on an expotition to the post box, some miles away
remembering to do all this, or have its multiplicity of components in place, in time for the org to receive it (which I often fail to do)
Wondering of the Postman has been eaten by tigers again, or whether the routesheet will arrive in time
getting the routesheet in a paper form so it can't be reformatted or jigged about with
No none of it is insurmountable, but it's a hell of a lot more faff than just clicking.