A common problem people have been reporting is the inability to reformat an APFS drive as something other than APFS. It appears in Disk Utility that you can only erase a disk and keep it as APFS. However, a simple switch in Disk Utility is preventing you from selecting the device rather than the volume. Once you select the volume, you can reformat however you like.
Dan: Typically, you want to do it when you have a different use for the drive. For instance, if you have one formatted APFS then it only works on recent Macs with recent versions of the OS that know APFS. But if you want to use it with an older Mac, or a Windows machine, you would reformat it as HFS (older Mac format) or ExFAT (Windows), etc.
What is the benefit of re-formatting or erasing a thumb drive?
Dan: Typically, you want to do it when you have a different use for the drive. For instance, if you have one formatted APFS then it only works on recent Macs with recent versions of the OS that know APFS. But if you want to use it with an older Mac, or a Windows machine, you would reformat it as HFS (older Mac format) or ExFAT (Windows), etc.