Update: I made a mistake in stating that only AMOLED devices have the background photo feature. Some LCD devices do have it, but it seems to be only the chosen few.
One of the greatest selling points of modern Lumia devices that screams convenient luxury is the Glance screen, which shows the time and pertinent notifications of your choice even when your phone is locked. If your phone supports Glance in Windows 10 Mobile, it'll be found buried in the Extras section of the settings menu.
The first item allows you to select how long you want Glance to display after the screen's been locked. What on God's polluted earth the 30 second setting is supposed to be for is beyond me, but if you have a Lumia device with an AMOLED screen, such as the Lumia 925 and the newer Lumia 950 and 650, Glance consumes virtually no power, so there's literally no reason not to leave at Always On. In my experience, even with LCD based Lumia devices Glance consumes negligible amounts battery.
If you find Glance's shine to be distracting for your night time beauty sleep, you can also choose the color with which it will be displayed at night time, and when night time is for you.
You can also control whether to show date, notifications, and detailed status which directly corresponds to lock screen settings.
One particularly unique Glance feature found only on Lumia devices with AMOLED displays, basically the ones I discussed above, is that you have the option to make your lockscreen background photo on the Glance Screen in either black and white, or a limited selection of colors. What I mean by this is even though it will show your background permanently, the fidelity isn't quite as good as if the screen were on. Also note that having a background on in this manner adds significant strain on your battery.
It's important to note that this feature, even while on, will only work at night time if Night mode is off.
To me, Glance is one of Windows Phone's biggest unique selling points, and I'm glad it survived the transition Windows 10 Mobile. Now we just need to get double-tap-to-wake on the Lumia 950 and 650. Which may not actually be such an impossible task after all.