O, that is a good one!
I have to honestly admit that I have no idea whether this brings any advantage and if so, how much. I just always assumed that if I was already using redis - and redis is really designed for speed - that it would bring some advantage. 
It is much more important to define igbinary as the serializer (which is automatically the case if php-igbinary is installed on Ubuntu/Debian) to speedup php-redis. Compared to the normal php serializer or json serializer, this has up to 50% advantage in memory consumption and up to 30% of speed.
In the packages from Surry (including the ‘normal’ Ubuntu and Debian packages), igbinary support is compiled into the php modules redis and memcached. That is not the case with the php modules used in the nextcloud-vm (HanssonIT).
If you are using such a nextcloud-vm, run php-updater, that script will detect if the modules are built with igbinary support and can fix that.
To use igbinary as a serializer for apc, “apc.serializer=igbinary” must be explicitly commented out uncommented in the file “/etc/php/$php_version/mods-available/igbinary.ini”.
Much and good luck,
ernolf