I'm a little unclear on when you can (or must) use the object infixes. The Tips and Notes kind of make it sound like they should be used when the object is implicit and/or definite, sort of like the Hungarian definite conjugation of verbs, but most of the examples from other lessons don't have them, whether the object is definite or not. Is there a situation when you absolutely have to use the infixes?
The use of object infixes will definitely depend on context many times - for example, if you wish to omit the noun in a construction after it has already been identified, you can use the object infix. I read/am reading the book - Ninasoma kitabu, but if I already know you're referring to the book, you can say - Ninakisoma (I read/am reading it).
But, when you use prepositional forms of verbs, you always need to include an object infix. I am reading/read the book to/for you or I am reading/read you the book - NinaKUsomea kitabu. The object is the noun receiving or being manipulated by the verb in this case.