You dudes (some of you) are gong to make me old(er) before my time!
Alright. Let's put this one to bed (from my side anyway).
I'm no qualified chemist. So I concede that maybe, possibly, the end rock or crystals (method dependent) formed are the same substance.
And I think
@unodelacosa has summed it up nicely above and as quoted below. And this person is either a chemist and/or knows his/her oats from a chemistry perspective (and not just when it comes to Cocaine from what I gather).
Did I get decent Crack rocks in the day (late '80's thru most of the '90's)? Certainly. Definitely. With those Crack rocks: same effect? Yes. Bellringers were the norm not the exception. And these Crack rocks where pretty white in color and, ironically, also used to melt clear on the gauze. And they were hard and brittle. And you could hit them time after time without feeling like shit. And the only residue formed in the pipe was dry and powdery and you could scrape the pipe and hit the stuff and same effect.
Fast forward to the time where this changed. Crack rocks became darker in color, more powdery, and most certainly didn't have the punch of the above no matter how many hits you had. When melted they'd melt as a milky substance on the gauze and sometimes even a brown substance and that stank to high heaven sometimes. And there was usually little to no residue left in the pipe and most times if there was it was a horrible, oily, black substance. And scraping the pipe wasn't possible i.e. only way to be greedy and try get another hit was to push the gauze up and down the pipe to catch this shit. And more often than not it'd make you cough and splutter and also had the propensity to ignite. And even if you got a mild rush: it didn't last long, certainly wasn't smooth, and resulted in jitters, paranoia, and generally it was just shit. And oddly enough: while this was all going on the HCL being delivered was also off color, smelly, burned the shit out of your nostrils, little to no anesthesia, no drip, just, again, plain shit. And it was at this time and for these reasons I started a) cooking with baking soda myself (and ended up with the same crappy results) and b) going the chemical route.
Chemical route: back to the good (and even better) stuff and effects. But the loss was horrific. By that stage I was lucky to be getting 200mg of freebase from 1g of HCL. And that is no shit. So the problem is obvious i.e. false economy (to say the least). Not to mention the patience and restraint required in order to wait for the shit to dry proper (I didn't use lamps i.e. just let the shit dry by itself on a glass plate and sometimes that took a LONG time especially during Winter or when it was raining).
So that's my story (albeit only from an experience and anecdotal perspective).
So is there a difference between Crack and freebase? Technically and chemically maybe not. But in practice and with shoddy and unscrupulous cooks and crooks and crap HCL to start with: yes there is.
And one fine day I will do this test on HCL that I KNOW to be unadulterated and, in theory anyway, the loss (by weight) should be no more than 10% max. going the chemical route.

If for no other reason than to prove a point of course!
I leave you with a gift of sorts i.e.
David Lee's Cocaine Handbook which, I'm told, is getting harder and harder to come by nowadays. While it may be dated: it's a good read and served me well back in the day. And if you take things back to basics: it's as relevant today as it was back then (in spite of some new twists along the way since then) (but some of those covered in my threads on the the topic). Sorry for the scan and layout i.e. this not my scan or copy or upload (my original went missing years ago) (I think I tossed it when I gave this all up as a bad job). Some may perceive it as a harm reduction resource. Others may perceive it as an instruction manual. Take from it what you will!