Question about facebook group posting

Hey guys,

Have a question for you, I am still new at this, I am starting to use MassPlanner for facebook group posting, I have already see the limitations, I am planning to use 10 accounts and post on 10 groups everyday with each one of them. As I am new here, I don't know why most of you recommend to buy a domain and hosting? I am a bit confused with this, what would be the domain for? could you help me with this? would really apretiate a hand

Do anyone knows? or at least refer me to a post where this information is explained?