I have a doubt about databases, if its better use one table with repeated values or with null values, or its better to create new tables in a 1 to 1 relationship.

For example, in a conferecence management software, a user can register and can create conferences.

So, in the user profile the user can access a link “conference creator” to edit informations related to a user that create conferences, for example he can store a different email to receive notifications relative to conferences he creates. But in his user profile there is also a link “participant details” to access a page where he can edit some informations related to a user that registers in a confernece, for example instead of the user always introduce the information needed to generate an invoice when he register in a conference, he can go to his profile and store that information, for example he can store in this user profile area a different email to receive the invoice.

So its ok to have just a user table with repeated columns like:

User: name,email, password, emailSendInvoice, emailReceiveNotifications, etc 

But it is possible to email, country, emailSendInvoice and emailReceiveNotifications be the same most of the times.

Or its better have different tables like:

User: name, email, password ConferenceCreatorData: id_ConferenceCreateData, user_id, emailReceiveNotifications ConferenceParticipantData: id_ConferenceParticipantData, user_id, emailSendInvoice