Developer previews of the latest version of Android are a good way for developers to get an early look at what changes are due to take place and prepare accordingly to deal with those changes. However, the other benefit of early preview versions is that anyone with a compatible device can also get a sneak peek at what the next evolution of Android will look like. Of course, this does mean having to sacrifice aspects like stability in favor of the new features, as well as having to be familiar with flashing the latest image on your device.
Although, Google did look to somewhat circumvent the flashing element this year by launching an Android Beta Program, which essentially means you can enroll your device and have the latest developer preview sent over as an OTA and update like any other update. In fact, Google also recently confirmed that if you flash the image, you can still receive the next developer previews as an OTA update as well, providing you do enroll in the Beta Program. So in short, once you do update to any version of Android N, you should see all future updates coming as an OTA. That is, unless you decide to turn off system updates altogether.
It seems with Android N, you can actually turn off the ability to receive future system updates. The option to do so is listed under "Developer Options" where you can simply toggle off "Automatic system updates". After which, it is presumed you won't automatically receive any notifications about updates until you toggle the feature back on again. The obvious benefit is that you can delay an update that you are concerned is not stable enough and will not have to worry about the continual prompts to update. Although, for those running the developer preview of N, as this is an early draft version, it would be expected that most people would prefer to receive the next (and presumed more stable) version as soon as possible. So this is likely to be a feature more relevant in the final release. Although, its positioning under Developer Options does raise the question of whether it is a feature which is intended for a general and final release. As it would be presumed that a system update pausing feature would be more suitably positioned under the System Update section of settings. Either way though, if you are running the developer preview and do want to turn off system updates, you can.