This reference section exists to help you plan out your approach for the different methods of play - which crops, trees, and animals you will use depending upon the mode of play that you are presently pursuing.
During XP oriented play you will want to focus upon the higher-XP Items, particularly Prized Animals, bearing in mind that as you begin to develop a population of Prized Animals with exceptional XP you should not sell them off, but place them into storage when you shift to a money-focused play style.
The same basic approach applies to both crops and trees, less so with trees really because once you begin to deploy those into groves you tend to hold on to what you have just being practical, but for crops you definitely want to pick and choose which will give you the best results.
As you select the different crops to grow you should also bear in mind what you can do with the resources that you are producing in doing so - as the initial intake of XP and revenue can be easily doubled or tripled by Crafting with those resources. There is a synergism to all of this and it starts with being aware of what each unit produces, and that is where this reference section will serve you best!