I've seen the cut and dried version of what Time for Print (also called 'Trade for Print' by many) means on Wikipedia I was wondering what it is and what it means for the photographer and model alike.
A big part of it, in both cases, is about portfolio building and exposure.
Becoming established in the industry, especially when it comes to fashion or similar types of photography is challenging. Photographers without a strong collection of images will struggle to get gigs or get gigs that pay at all decently. So, for them, establishing this portfolio will help and so many will offer aspiring models a trade of images for their time in front of the camera.
Like the photographer, models need samples of their work to submit to various agencies or companies looking to do a shoot. These can be harder to come by when doing a professional work, and so cutting a deal with an aspiring, or even established, photographer for images and rights to use helps provide these shots for when needed.
So, it means the same thing to both, really, just for different purposes. It's also, in addition to the portfolio benefits, and opportunity for both the photographer and the model to practice their trades without the pressure of a commercial shoot and other deadlines.
Anyways, that's what I've managed to gather on the subject. We have a few pros on the site who may have done this and might be able to shed even more light on the subject.
It can mean anything from a mutually beneficial bartering transaction to an ethical tarpit.
As John noted in his answer, both photographers and models (including actors, who are often part of a TFP arrangement) often have a need for a portfolio. Sure, it would be nice to have tear sheets (examples of published work), but getting the kind of job that will get you tear sheets means proving that you can do it. A portfolio is a sort of resume of merit until you get tear sheets -- then it becomes a resume of experience as well.
I usually had a particular type of shoot in mind -- something that could get me work in a particular niche or fill a hole in a submission for juried professional accreditation (such as would be required for full membership in PPOC or CAPIC). For actual client work, I would always pay for models, but they can be pricey for speculative shooting adventures.
It was always my policy to make sure that the other party got something of real value. For models that had an actual chance of becoming working models, that meant putting together a decent comp -- not just throwing a couple of prints from my shoot at them. That, of course, meant shooting outside of my original idea, but a head shot and pics from a single shoot (same clothing, hair and makeup) aren't nearly enough to get an appointment for an interview with a real agency.
I saw a lot of sharks in the water looking for young girls with stars in their eyes in my day. As often as not, they'd wind up paying someone else for the privilege of appearing in low-budget porn mags without their knowledge. They always seem to be willing to believe that full frontal is just part of camera testing. I don't expect that the situation has gotten much better. I would much rather have done a bit of extra work and sent prospects with a chance to Ford or Elite (they were the only reputable agencies with local reps in Halifax at the time) with enough of a book to get in the door than to let them swim those waters.
I was shooting film and hand-spotting at the time, and I'd give them an eight-page 8x10 book (a small B&W head shot for a stats page, a full-page colour head shot, two full-page, full-length shots with different looks, and four composited pages -- there's a lot less retouching to do on small comps). That may have been a bit much back in the day, but in the digital world, there's no good reason to provide much less.
Actors would get a number of headshots -- the requisite classic (3:1 Rembrandt for guys, 2:1 butterfly for girls) and a few with different lighting/moods. These were generally B&W -- the industry didn't go much for colour in those days.
Aspiring models who may have been right for my shoot but who didn't stand a chance in the fashion/beauty world would get a bit of a reality check up front, and the best pictures I could give them if they wanted to follow through anyway. I like to think that I kept a few of them away from the seamier side of the "agency" business. I often found that "ordinary folk" would get into the groove for a conversation piece to hang on the wall -- they may have had exactly the look I wanted, but weren't on the verge of having the slightest consideration of beginning to think about modelling. Throw in a couple of "nice" pictures for Mom, Gran and Grandma, and the deal is done.
I never did time for prints for any work I expected to be able to directly profit from. That's my own personal ethic. It's one thing to do a bit of quid pro quo, but if I know that my quid is worth money and your quo is little more than a lottery ticket (especially if I have a pretty good idea that it's a losing ticket)... well, my clock doesn't turn that way.