Parallax error isn't a helpful thing in photography. It's mostly a nuisance and an annoyance.
Older cameras used to have this problem: The old film cameras normal people, non-photographers, used to take casual photos on vacation and things like that, family photos of trips and that stuff, those cameras always had slight parallax error. The viewfinder wasn't looking through the lens, it was above the lens so what one saw and what one shot was slightly different.
SLR cameras have no parallax error at all because you're looking through the lens. That's where the name comes from. The 'reflex' is based on the mirror used to see through the lens flipping up to allow the film or sensor be exposed to light from the lens.
It's why they're a bit noisier and you can't look through the viewfinder when you click the shutter.
Point and shoot cameras, digital ones, use electronics to display the scene through the lens on an LCD screen instead of a viewfinder, so there's no parallax error there either. The point is to, well, point and shoot.
My constant problem with the error, though, has nothing to do with the camera itself and all to do with the panoramas I've been trying to make over the past several years.
I've written about panoramas and generating them on here before. Originally I'd explained that using Hugin was much easier than PTGui. I've had more experience with PTGui to know now that it's perfectly possible to generate your own control points from scratch. Just go to 'Advanced.' Either way, I've also found that PTGui isn't actually as useless as I originally found it to be. As long as it was an easy panorama with nothing close-up.
The real problem, however, that has probably always been at the root of things, is parallax error.
I've seen amazing panoramas, equirectangular, all over the place and created using PTGui. They're spectacular and amazing, and have no errors. I'd be in wonder at how they do it. On Flickr there are entire photostreams that are only dedicated to those kinds of panoramas/planets. They're all, well, perfect. And they're panoramas that were taken in all sorts of places, both easy and difficult positions. There's one Flickr user that uses a 10mm lens, does them hand-held, only takes ten images, and uses Hugin, and his results are incredibly perfect.
Recently I got myself a 6.5mm fish eye lens, for my birthday. It's full-frame (not circular) and it's nice, although third-party (I have to manually focus myself, as well as the aperture). With this acquisition, I thought I'd have a lot more ease of stitching. Less images to have to take as well as the fact they're already distorted should make it almost no burden at all.
I was quite wrong.
The thing is, with fish-eye lenses, because there is distortion to begin with, the potential for parallax error is a lot higher. It's much easier to have things change between images because it's already distorted visually enough. Everything just got harder for me instead.
In my case, I've got almost everything to make panoramas as flawless as that Flickr user. I just need, as any panoramic photographer needs, a special kind of tripod that eliminates this parallax error problem.
The way it works, the end of the lens doesn't move anywhere. It just changes viewing position - without doing anymore than rotating. When I use my normal tripod head, my camera revolves around the central point when the end of the lens should be positioned there and rotating at the centre of it.
The two images (which should be next to each other but won't let me put them as such) explain parallax error in action: in one image the corner of my gazebo is shown with my shed at the left in the background. Then, when I moved the camera for the next image, the shed was more central in the background. The pillar itself is at a slightly different angle. The software, when it stitches, has trouble arranging where the pillar should go in accordance to the different backgrounds of each photo, and ends up either multiplied, cut up in sections, or partially erased.
Until I get the proper tripod head, I will have these problems. Panoramas like this can be, and are, tricky things to work with. Panoramic tripod heads are expensive; when I looked online the nodal ninja head everyone uses was about $200.
I won't be investing into that until after I begin college.
For now, I'll keep trying my best in panoramic photography. It's not like I am destined to fail at good images just because I don't have this particular piece of equipment yet. But if you're going into creating those cool, perfect 360/180 degree equirectangulars, a fish-eye and panoramic tripod head are going to be your best friends.
...And the software and minor knowledge of it as well.
Parallax error is your worst enemy.