Is it safe to remove APFS containers?
TL;DR: To do a perfect clean wipe and reinstall in APFS now you need the terminal in recovery in addition to Disk Utility. It has to do with the container which is the new base volume scheme in APFS. 

For your information, I upgraded my 2017 MBP to High Sierra since beta 9, and decided to clean wipe and reinstall immediately afterwards (makes me feel better reassured with all the APFS conversion). I checked the output 

diskutil apfs list


both before and after, and realized how my recovery volume inside the new APFS container has grown in size from ~500 MB to 1.1 GB.

Not letting that go, I did another clean install when the GM candidate arrived and sure enough the recovery has grown by another ~500 MB to 1.6GB. Not that this is likely going to happen to you but disk space is still disk space - Macintosh HD actually shrinks even under the shared volume scheme. With the arithmetic progression I'm pretty sure the recovery volume is not being overwritten but rather added upon every clean install. 

After some time figuring how some of the things now work in APFS I found the caveat. When I wipe my disk through Disk Utility within recovery I can only wipe the Macintosh HD volume that sits within the 

Container disk1


but not the container or the disk itself like we've been doing pre-APFS. Even when you show all volumes in Disk Utility you'll get an error message if you do that. So the other 3 volumes (Preboot, Recovery, VM) are untouched - I was just doing a somewhat "unclean wipe". 

The workaround is, with APFS now we have to open up terminal under utilities in recovery, then do

diskutil apfs deleteContainer disk0s2


assuming your container is linked there. Now it will create a single empty volume named "Untitled" under your physical disk media as shown in Disk Utility. 

We're not done yet - you have to go to that disk, e.g. "APPLE SSD...", then click erase in APFS format named Macintosh HD (or any name you wish), in order to set up the correct APFS container structure ready for you to install the OS back in place. The other 3 volumes sharing the container will not be there yet, but fear not, they will be automatically created when you install the OS.