"A mi me gusta" or "me gusta"

"A mi me gusta" or "me gusta"
 

I'm studying Spanish on Duolingo and have a question.
Sometimes it requires me to use, for example, "a mi me gusta"
and sometimes it requires me to use, simply, "me gusta".
The question is, when do I use either one? In what circumstances?

Thanks for your help in advance,

Don

Both phrases are valid, the only difference being that when the indirect object a mí is included, emphasis is being given.
The indirect object pronoun me can be used alone (without providing the associated indirect object a mí), because there is no ambiguity; the only possible meaning is 'to me' (a reference back to the speaker himself).

Likewise, when the indirect object pronoun te is used, the only possible meaning is 'to you' (a reference to the person being addressed by the speaker, using familiar form). Therefore, including the indirect object a ti simply adds emphasis.

When the indirect object pronoun is le, however, ambiguity can occur. If it is uncertain whom is being referenced, the speaker should provide the indirect object to clear things up for the listener. For example, the phrase le gusta a mi mamá is crystal clear. To whom is something pleasing? My listener can only conclude that it is my mom.
By the way, the indirect object can precede or follow the verb:
A mi mamá le gusta. = Le gusta a mi mamá.

Ambiguity is also possible when using any plural indirect object pronoun.

Thanks Rusty for taking the time and making the effort to respond. I appreciate it.

Don

You're welcome! I hope the information was useful.