UseOnceTo

UseOnceTo() is just a convenience method that you can use. It lets you get rid of the code necessary for creating a Session via the factory method of the Database.

db.UseOnceTo().Insert(customer);

var customers = db.UseOnceTo().Query<Customer>().Where(c => c.Points > 10000).ToList();

NOTE!

You should only use these methods if you are doing ONE Read or Write operation. If you do several in a row, YOU SHOULD CREATE A SPECIFIC INSTANCE OF Session. The reason for this is that UseOnceTo() encapsulate the creation of a session under the hood. And since each of this opens connections to the database, you could affect performance if you call UseOnceTo() repeatedly.

Alternative

You can also make use of db.WithSession():

db.WithSession(s => s.Insert(customer));

var customers = db.WithSession(s => 
    s.Query<Customer>().Where(c => c.Points > 10000).ToList());