Is the Indirect Object Pronoun needed when the Indirect Object Noun is a thing?
Is the Indirect Object Pronoun necessary when the Indirect Object Noun is NOT a person?
Le agrego azúcar al té. I add sugar to the tea.
(Ella) le está agregando azúcar a su té caliente. She is adding sugar to her hot tea.
(Ella) le agrega pimienta a la sopa. She adds pepper to the soup.
Gracias por la ayuda.
6 Answers
Los pronombres de complemento indirecto representan a la persona (o personas) a quien se hace una acción. El uso más común es para referirse a personas. También es posible usar estos pronombres para referirse a cosas inanimadas; por ejemplo:.
Le eché agua a la sopa.
I believe that it is possible and probably common to use it, but I believe grammatically that the i.o.p. is not obligatory in this form.
Where it is obligatory to use the duplicative pronoun, is if the i.o. or d.o. precedes the verb, or if the d.o. or i.o. is a personal pronoun, no matter where it falls in the sentence.
Si Tosh, perfecto 
Like "lo tiene todo calculado".
Le gusta levantarse temprano.
Le tiene miedo a los perros.
Hey have you already been to these sites that I'm finding for you? lol
The first one had the tea to the sugar example and now here's the pepper to the soup! 
The way I look at it is you want to try and make the most sensical sentence as is possible... To use your example "le agrego azúcar al té" now does it still make sense if you omit the indirect object noun? Yes, it does. "le agrego azúcar" "I add sugar to it"...dont be afraid of redundancies in spanish. Spanish loves double negatives and other reduntant things lol I always add an indirect object pronoun if I can for the sake of clarity...afterall being understood is what its all about.
Seems like it's optional but more natural to use it if these people on this forum knew what they were talking about je je
So in conclusion I'd say yes, if you have an direct object in the sentence as well and you're stating an indirect object it is preferred to use the 'iop'
