Late communication with support staff (I'm thinking IT support in particular, because that's my area of experience) leads to poorer service. It's not because they're bad at their jobs - far from it, in most cases - but when you only call them at the point where it's last-minute urgent, they can't set priorities in their work. They have to drop everything and focus on you, and then focus on the next catastrophe and so on. It leaves no time to keep the system as a whole in working order. It also means that your service is going to remain in its worst possible, barely-functional state at all times, because none of the issues are going to get fixed until the last minute.
I see it in software development, too. Clients will sometimes withhold information on requirements until the last minute, either to avoid "overwhelming" the development team or to manage the sequence of development. Neither one works very well, because decisions can only be based on what is known so far, and sometimes a wildly different decision would be made with all the information up front. If a developer doesn't know that, for instance, the next requirement up from "get this working for one user" is "now make it work for my whole team", a decision may be made to work on a single-user-focused platform like Access rather than something suited to teams.
The lesson is to do as much communication as possible up front. That way, everyone knows what's coming, conflicts come up right away when they're cheapest to fix, priorities and plans can be set and everyone knows what everyone else is thinking. Even if you don't know what's coming, communicate what you can. I promise it will go better that way.
Mokalus of Borg
PS - Some things will still be missed, I know.
PPS - Mostly it's because some things seem obvious to one person and not to another.