What he means that when you plant and harvest the seeds manually, there's a chance that you can get some weak essence (one of the crafting essence tiers), nature essence(used for a few special items), and (configurable) an extra seed. So if you plant 8 seeds and have it have a 25% of a seed, you will get an average of 2 extra seeds when you harvest. Automated methods like MFR harvesters or TC golems however do not allow those extra drops (though at least for me it seems the seed drop chance still work) so if you need the extra essence or need the nature essence you'll have to harvest manually.