Why bad support matters (war story included)
Once upon a time, we wanted to buy an 'appliance' style machine. We did our research, made a choice, and put our choice through a bunch of qualification and testing in what we figured would be our production configuration. At the last minute we decided to try our test unit out in an odd configuration, one that we weren't planning to run in production, just to see how the overall system would look in that setup.
It exploded, by which I mean 'the appliance locked up'. We had support for the test unit, so we called up the vendor. What followed was one of the worst support experiences I've ever had, with the vendor doing everything it could to not support us short of outright telling us to go away; there were interminable conversations with people who didn't seem to take notes, the usual belief that we were clueless, there was the 'that's not a supported configuration' excuse (multiple times), and so on. By the end of the experience it was clear both that the vendor wasn't going to fix this bug and that the vendor wasn't going to provide any support at all (beyond repairing hardware faults) regardless of what they said.
(The latter is not unusual in practice regardless of what people say in theory.)
This led to me having the experience of sitting around a table with a bunch of other people here, trying to decide if we were going to stay with the appliance. I want to note here that we really wanted to use this appliance. It was clear to us that it was our best, most affordable choice for an appliance solution to the problem we were trying to solve and all other similar appliances we'd looked at either cost too much or were clearly worse than our choice.
(We'd also invested months of work into the appliance-based solution at this point, which was a consideration.)
Our decision was no, we couldn't use the appliance. You might think that this would be a slamdunk, but that's not the case; after all, the bug we'd found wasn't in anything we were planning to do in production. Why should we let one ultimately unimportant (to us) bug and a bad support experience disqualify an otherwise solid unit?
We reached this decision by deciding that where there's one bug, there's quite possibly going to be more than one. We had no guarantee that the next bug to turn up wouldn't be in something that we were using in production, and if we hit an 'appliance locks up' bug in production and got the same level of non-support we would be totally dead in the water. We would have spent tens of thousands of dollars building an environment that didn't work and that failed explosively just when the entire department was depending on it, and we'd have done so knowing that this was a real possibility. We decided that we could not take that risk, even if throwing out the appliance-based solution could cost us a lot of time and a not-insignificant amount of money.
(In the end it merely cost us time.)
That is why bad support matters, sometimes a lot. Using something from a vendor requires trust; you need to trust that the equipment is going to work and you need to trust that the vendor will fix it when it doesn't. Getting bad support in a situation like this means that both elements of this trust have been destroyed; the equipment (sometimes) doesn't work and the vendor is not going to fix it. The only time you can safely continue to use the equipment is when you are absolutely sure that it fully works in your specific situation and thus that you won't need vendor support.
Sidebar: the commercial cost of bad support
Bad support cost this vendor tens of thousands of dollars worth of direct business (in addition to all of the time their support people, management, and sales chain spent in arguing with us and being yelled at) and who knows how much follow on business from us and other people within the university. At a stroke they went from a centerpiece of what was going to be a fairly visible core system to someone we recommended against having anything to do with.
(We've not bought anything else from them and I doubt we ever will, even though this incident is now years in the past. They have a reputation now.)