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Arch Linux keeps things simple - it's lightweight, without the cruft of most other distributions, and completely flexible. These traits make it a popular distribution with many more experienced Linux users.
SpecsUpdate
Pros
Pro Excellent documentation
Arch's goal of simplicity means there's usually one preferred way to get things done - through organized and well documented configuration files. This focus, combined with the community's recognition that configuration files can be intimidating, has resulted in excellent documentation that's accessible to newcomers, and very instructive about how Linux actually works. The documentation is often so thorough that, when searching for solutions to problems while using other distributions, such as with video card drivers, oftentimes you'll find the most effective solution in the Arch Linux wiki or on the forums.
Pro Fast and simple package management
Pacman has performance advantages over apt-get and yum in both database operations (thanks to being written for speed) and download times (by virtue of using better mirrors than other distributions tend to select by default). There are also fewer default repositories to download from, and all package management is combined into one tool instead of being split into dpkg, apt-get, and apt-cache like on Debian distros.
Pro Simple by design
Arch linux is actually incredibly simple. Its really just a partition scheme, package manager, Linux kernel, file system, systemd and the bare minimum of utilities needed to easily set up your hardware.
This makes it super simple to build your desired system using binary packages because there no bloat getting in your way when installing or configuring packages.
Pro On avarage only 1 manual intervention needed a year now.
The comments about issues with upgrades are over exaggerated.
Those comments assume that : A) They happen often, B) you are using a specific package with an issue, C) that package maintainers can't release a patch to the package that will work around the issue for you, and that D) Manual intervention or system recovery from such issues is hard to fix.
On average once or twice a year a user may have to cut and paste some commands in the terminal to fix an issue, but that's about it. Additionally any system recovery required from such missed interventions is easy, just follow the wiki and make a live usb if your using a desktop or laptop.
Pro Excellent package management with the AUR
The AUR is a repository with a very extensive catalogue of build/install scripts that are contributed by users. While these scripts are inherently less secure than conventional packages maintained by a distro's authors, it's still way easier to verify the security of install scripts than it would be to write them yourself. It's very usefull.
Pro Helpful community
If searching through the wiki or the forums for any problems turns nothing, any question on the official forums, Arch subreddit or the IRC channel will be answered within minutes. There will probably be no hand-holding however, Arch users prefer to point anyone to a resource that may help them instead of trying to outright solve their problem in a forum thread. This is quite helpful for people who want to really learn how their system works but also for other people who may stumble in that thread considering how most problems don’t have a universal solution.
Cons
Con Toxic meme and 4chan-centered community
The toxic community that comes with Arch affects almost every action you have to take online. Good luck looking for an answer to a major problem, and having to "ask correctly", or be told off by a memelord. For fun, sure thing, for serious or production work? Never in a million years.
Con Fragile packages
Updating an Arch system is always a gamble. The problem could be as simple as a package having a bug causing a program to crash on start or it may be something bigger like the WiFi or Bluetooth no longer working. There is also the slight chance the system may not even boot at all after a large update.
If the user does not plan to read the forums weekly/daily or update fairly often, things can go wrong very fast.
Con Documentation only makes sense if you know how to adjust it
While the documentation is a very valuable reference for experts, the recipes often don't actually work on your own computer. Some articles are outdated, incomplete, contradictory or duplicated. Only if you are expert enough to know which steps to skip, to adjust or which other documentation parts to plug in, you can make it work.