The Giant MOKFs are done-in-ones but the stories are reflected in the continuity of the regular series.

Cei-U!
I summon Rufus T. Hackstabber!

The Giant-Size books are fascinating. As I recall, Marvel's plan was originally to publish a line of "Super-Giant" comics that would be more like DC's 100-Page Super-Spectaculars, 100 pages for 60 cents. I'm a little fuzzy, but I think they announced plans to have both the Super-Giant and Giant-Size comics running in addition to their regular size line. Either that, or the Super-Giants were downsized before launch. The Super-Giants would have one new story and some reprints, at 60 cents, while the Giant-Size comics would be all-new for 35 cents. Eventually, the plan they settled on was to publish two Giant-Size comics per month, with rotating headline features:

Giant-Size Superstars would star Fantastic Four, then Spider-Man, then Conan, and then repeat the cycle.
Giant-Size Chillers would feature Curse of Dracula, then Werewolf By Night, then Man-Thing.

The first issue of each was published--Giant-Size Super-Stars and Giant-Size Chillers--but then the plan was changed again. Instead of Spidey and Werewolf headlining the second issues, they instead got their own first issues: Giant Size Superheroes starring Spider-Man and Giant-Size Creatures with Werewolf By Night.

When the next round of headliners came up, plans changed yet again: instead of an umbrella title like "G-S Super-Stars" or "G-S Chillers", they more sensibly went with Giant-Size Conan and Giant-Size Man-Thing. After all, they no longer planned to rotate the features, so why have the overhead of the longer names? Consequently, the second issues of three of the initial four were titled "Giant-Size Fantastic Four", "Giant-Size Dracula", and "Giant-Size Werewolf". "Giant-Size Spider-Man", however, started over with a new first issue and a new premise: Giant-Size Spider-Man was really Giant-Size Marvel Team-Up, but it featured team-ups that were a little more "special" than those running in the monthly, regular size issue. Dracula, Master of Kung Fu, and Doc Savage were characters that were on the periphery of the Marvel Universe, if they belonged to it at all, and the Punisher was a villain, so those first four issues had a distinctly different vibe than MTU did. And acknowledging that this was really a team-up book, Spidey took a break from MTU every month that the Giant-Size was published, letting the Human Torch headline the regular sized comic in those months.

Another change at this point was that the books got bigger: 68 pages for 50 cents with one new story and one or more reprints.

One interesting fact about Giant-Size Chillers featuring Curse of Dracula: this feature was originally advertised as "The Victims of Dracula", and was scheduled to run in Supernatural Thrillers. The focus would be on characters whose lives had been affected by Dracula--presumably mostly people he had turned into vampires, but in the first issue featuring his daughter, Lilith. This conceit appears to have been dropped with Giant-Size Dracula #2. I'd have been interested in seeing what they might have done with that concept.

Giant-Size Kid Colt was also interesting, because issues 1 and 3 are team-ups with Rawhide Kid and Night Rider (a.k.a. Ghost Rider). These may be inventory stories from the cancelled Western Team-Up, which mysteriously stopped after a single issue.

In the second year, Marvel decided to debut three new series in the Giant-Size format, with X-Men, Invaders, and Super-Villain Team-Up. S-V T-U was the first, and it made it through two bi-monthly issues, but at that point the Giant-Size books were winding down, and the three issues reverted to regular size series, with X-Men resuming its original numbering, the other two starting over with No. 1. The line now actually expanded, with Giant-Size series for Marvel mainstays like Iron Man, Daredevil, Hulk, Thor, Captain America, Power Man Dr. Strange, and Captain Marvel, but these were reprints, as were the final issues of some of the once-all-new series, like Avengers, FF, and Conan.

I would usually buy them if I was following the regular series unless they featured the a totally different creative team that I happened not to care for. Can't recall off the top of my head is that happened much but I think it did now and then. But there was obviously no way you'd ant to miss a Giant-Size issue of, say Howard the Duck, if it was written by the same person doing the regular series, in this case Steve Gerber.

Okay, thank you. I'm still filling out my run of MOKF but have yet to get any of the Giants. That scenario may work out better anyway since you aren't missing out on any story conclusions. 

They're fun reads but yeah, you won't miss anything of, for example, that first big Fu Manch epic by Moench and Gulacy, as it all unfolded in the regular series.

As a kid, trying to read hard-to-acquire silver-age stuff, I welcomed GS stuff. If a GS had original content, all the better.