Boon is a blessing which everybody wants. A curse is something which nobody wants. In this post, I will combine my knowledge and experience in teaching you more about them in detail.
First comes boon. Everybody prays to GOD for boons. Most of the time, both the presenter and receiver of the boon are put in advantage. The exception comes in cases where the receiver of the boon misuses it for selfish reasons. For example, there are many stories in our mythology that demons who received boons from Lord Shiva have become a headache for Him and it was Lord Vishnu who had to put an end to such demons. This shows boon given to a good person is beneficial to All parties, whereas in case of bad person it can endanger The Creation. Also, blessing an unfit person with a boon might put both, the presenter and the receiver, at loss.
Now let me talk about the curse. People curse when they are harmed, hurt or ignored. Cursing reduces the power of both the Curser and the Cursed. So, it is advisable not to curse as much as possible. When someone curses an innocent and righteous person, then such curse becomes a boon to the cursed. There is a story in Mahabharat which tells Arjuna was cursed by Apsara that he will be a eunuch for 1 year for insulting her. Arjuna was righteous and that curse helped him during Pandavas' exile where he lived as Brihannala for 1 year. At the same time, if the cursed retaliates or has negative intentions, then the curse is bound to happen. So, in order to come out of the curse, one has to be righteous and should not retaliate against the Curser. Instead, the Cursed must sincerely seek forgiveness of the Curser. At the same time, cursing someone must be avoided because GOD knows how to punish wrongdoers. GOD's punishment will be bigger than any curse. Cursing leaves a Curser powerless. If one curses someone intentionally and unethically, then The Curse will inflict the Curser directly or indirectly.
This post is a Boon even to the Cursed ;)