Possibly I'm an old fart about this (though I'm not really that old) but I'd discourage anyone from dropping out absent remarkable circumstances.
Here's the thing:
Personally, as an employer, hiring manager and co-worker not having a degree in and of itself doesn't mean a whole lot to me. Specifically, I've hired people with professional-level jobs--the kind you usually "need" a degree for--with little regard for whether or not they have a degree. Sometimes I've hired (or promoted or given a raise to, or, for that matter, laid off) the person with a degree. Sometimes I've hired/promoted/fired the one without a degree.
But here's what I've seen:
If you're _very_ successful, it doesn't matter at all. But you need a truly remarkable accomplishment to reach that state. Otherwise it _will_ hurt you, at least with _some_ people, at least _some_ of the time.
In particular, it will hurt you with:
- HR departments when they are deciding whether or not you meet the base requirements of the position, or what pay you should receive.
- You direct managers as they fight with HR about things like requirements and pay (or if they choose to fight for these things) at both hiring-time and promotion or annual-review time.
- Supervisors and middle/upper management as they consider which employees are likely retention/flight risks, and which are not. (and therefore which are likely to get perks as an incentive for staying and which are not-likely to get those perks, because they at least a little more "trapped" in their position).
I have seen all three of these things happen more than once. I've seen really good and smart and (largely) productive people get shafted over the long haul: not because of any one major decision that didn't go their way but because of a series of little ones over a period of years--decisions where they were disadvantaged, however slightly, but not having a degree. These issues come up for at least the first 15-20 years of one's career, in my experience.
Having a degree, if nothing else, demonstrates a certain amount of "stick-to-it-iveness". I'd guess that most people forced to make a a hiring or investment decision would at least pause to consider why candidate dwong didn't complete a degree program.
Unless (a) the thing you dropped out to do is pretty obvious and (b) in retrospect that was pretty obviously a smart decision,or (c) you've done something in the interim that overwhelms these other questions then many people when faced with hiring/investment decisions are going to at least pause and consider whether you have sufficient drive/commitment/ability to overcome obstacles over the long haul.
You may be more or less likely to run into people that care about the degree in some fields, but you'll run into a least some of them in every field. You may be able to accomplish something remarkable enough that no one cares about the degree question at all, but "I founded this web-based start-up. We did OK." isn't remarkable enough. You may be able to build a career for yourself (as an employee or an entrepreneur) where the opinions of the people that care don't matter, but bear in mind that until you reach of point of literally independent wealth everyone has a "customer" of some kind that they'll need to keep happy--a boss, an investor, a board, a patron, a client, etc.
I'd think really hard about whether the thing you are dropping out of a degree program for is truly worth it. It's not the end of the world. It doesn't even really close any doors for you. But it does make some doors a littler harder to open (and some a lot harder to open). Is doing your alternative to college right now and possibly limiting your options for the next 10-20 years worth more to you than delaying your alternative for a year or two and finishing school first? That's not a rhetorical question--I honestly don't know what the answer is for you. But I don't believe the people who say it simply doesn't matter at all. There really are some negative repercussions of that decision (just as there are negative repercussions to the decision to stay in school as well). You just need to figure out if the good outweighs the bad.
I'd also think really hard about whether "dropping out" and "not dropping out" are the only two options. Can you take a sabbatical/leave-of-absence/year-off/semester-abroad? Can you moonlight on whatever you'd otherwise be doing? Can you do school part-time? Switch to a different school? Switch programs? Find a program more in line with you passions? Go all-in and finish school faster?
(There is also value in the college experience and liberal arts education, but I'll leave that argument for another day.)
As practical matter, it really is _generally_ a bad idea to simply drop out entirely. If you were my friend or my kid, I'd strongly encourage you to demonstrate problem solving skills and find a way--however non-traditional that way might be--to make it work instead.