Google officially released the second developer preview for Android 8.1 earlier this week, and while it started with the software only being available in the form of Factory images and OTA images, it's now started to make its rounds to Pixel devices in the form of an over-the-air update so all you'll have to do is download the software package and then reboot your device to finish the installation, which will then move you forward to the second developer preview.
The software itself is just a little over 161MB for the Pixel, so that alone showcases that there isn't a whole lot of extra stuff from the first developer preview which was quite a bit larger in terms of file size for the download. That said there are likely to be some nifty little changes and goodies to look out for and as more time is spent with it those changes will become more apparent. Even if the changes aren't monumental they still usually end up being an improvement over the previous build which is reason enough to consider the update if you were already coming from the first developer preview, assuming you were having any issues in the first place.
If you're not keen on flashing system images to your device to load up the latest software, then waiting for the OTA update to make its way to your device on its own time is your best bet as it requires less steps for the entire process. Not to mention, if you like your software to be more on the cutting edge so to speak, then moving along with Google when it releases a new developer preview build lets you try out the incremental changes and test the software while its going through the process to makes its way towards completion. If you have a Pixel 2 or Pixel 2 XL, then you may have already received the notification about the Android 8.1 DP2 OTA earlier this week, and if you're a first-gen Pixel device owner then you may now just be getting it for the first time. The question is are you planning to install the second developer preview or will you end up waiting for the proper software push?