Like was said above, it is one of those border line cases. It will certainly not stop the board from functioning properly if
everyone codes properly. That's a big "if", though
In general, it is a good idea to make rules, that affect your database's data, explicit within the database. In this case, apparently there is supposed to be only one database row with a particular value for the column auth_option. If duplicate entries were to end up in the database, very obscure bugs might result, because code making use of the data is assuming there will be only one row, where there might be multiple.
People writing code to insert values into that table will have to check if there already is a row with that particular value, or delete any value that might be left, before inserting new data. One approach to stopping multiple values from ending up in the table is to basically assume that everyone will code properly. This is a very decentralized approach and prone to problems. If it does go wrong, the earlier mentioned obscure bugs can be the result.
The other approach, which generally is the preferred approach, is to have the database enforcing the rules that apply to the data within, i.e. making the rules explicit that were otherwise implicit. Marking the column UNIQUE, means that the database will make sure that the data in that column will in fact be unique, and will stop duplicate rows getting into the database, even if people write code that otherwise would result in an inconsistent database. It is enormously helpful to spot problems in the code, because it raises a flag the moment the "damage is done" instead of causing obscure bugs somewhere down the line.
Of course, this is very much a theoretical presentation of the matter, maybe there are specific reasons to not use these mechanisms. For example, I wouldn't know what the performance implications would be of marking a column UNIQUE (although I would expect that it primarily has implications upon writing a database row, which in this case only happens sporadically (I think?), and that reading of the table is not impacted).