I have a valid b1/b2 visa I obtained for the purpose of a conference last year, unfortunately I couldn't attend the conference for some family issues. Now I wish to use the visa this year, would that be allowed knowing that the conference has passed?
U.S. visitor visas are not canceled or revoked simply because you were unable to use them for your originally intended visit. You can use the visa and enter the United States at any time up to its date of expiration, for any legitimate purpose allowed by the visa type. For instance, if you have a B-1/B-2 visa you can enter for tourism or business visits as long as the visa remains valid.
It is still a good idea to bring with you documents that show that you intend to leave the United States and that you can pay the costs of your visit, as well as proof of onward travel, as you are likely to be asked for these.