Some problems you want to have. A huge firm signing up is definitely a problem you want to have.
I was first introduced to this concept by a colleague who was going to serve customers manually instead of us programmers automating it. I said he was going to have a major issue when lots of people sign up. He replied "That is definitely a problem I want to have, I hope I get completely overloaded, because then we have the money to automate it".
I guess it is related to Paul Grahams "do things that don't scale", but "problem I want to have" is broader.
Since then I always evaluate if certain problems are the ones I want to have, because then I know I can postpone them.
The problem is what zaroth outlined at the start of this thread: the big company doesn't start as your customer. They start out as "Hi, we're a Fortune 500 company and we'll become your Number One Customer if you jump through these hoops...before we sign a contract!" And you start jumping. And there are more hoops. And you jump. And they have a strategy change and blow you off for six months, then come back with a different set of hoops. And you jump. And you jump. And you've spent hundreds of thousand of dollars for the promise of getting that big customer, on the belief that they'll surely sign and that other customers of their size will follow.
And they don't sign.
And it turns out what you worked on for them isn't something other customers of their size really quite want. But if you jump through these hoops...
Supporting thousands of users from a huge firm, while only charging them $49, is not a problem you want to have. You're just giving away resources at that point.
$49 for thousands of users is basically free. For a CRM, a company with a 2000 seat license should be paying well into the tens of thousands of dollars a year, if not significantly more.
Better make sure they don't then so you won't have to support a large company that signed up because of the low price.