In my opinion, it is almost always necessary to extract the wolf teeth. I say "almost" because there are some exceptions. I will use two different situations (and mouths) to explain my answer.

Case 1
You have a young warmblood gelding (3 years old) that you are starting into training. You anticipate that your gelding will go on to become a successful dressage competitor. When I examine this horse, I would recommend that we extract the wolf teeth in order to ensure that the horse has a comfortable mouth during the training process. It is thought that the inner cheek comes in contact with the sharp, unopposed wolf tooth when the horse is bridled and worked on the bit. If the wolf teeth are not removed in this horse, it is difficult for you (or your trainer) to determine if your horse is resisting the bit because of mouth discomfort or "behavior" issues (I am young and I don't want to work). If the wolf teeth are removed and your horse has had their mouth checked and the appropriate work performed, and you know that their mouth is comfortable, you and your trainer should be able to say, "I don't believe it is in the mouth." Does this make sense?

Case 2
You recently purchased a 12-year-old Quarter horse gelding that you pleasure ride on occasion. You tell me when I am doing my physical and oral exam that your horse has no complaints, you ride in an egg butt snaffle and that your horse works equally well to the left and right and that there are "no issues." When I do my oral exam, I find two large wolf teeth. I would recommend NOT removing these wolf teeth, since they are not apparently causing any discomfort or issues for your level of performance for this horse. Does this make sense?

You also asked how often is it necessary to check a horse's mouth and perform dental care. This is a little more difficult to answer, since each horse is an individual. I include a dental exam in every physical exam that I do. Young horses (2-5 years of age) have rapidly changing mouths (shedding baby teeth, erupting adult teeth), and should have their mouths checked twice per year, having any appropriate dental care done at that time. Adult horses I normally check yearly; some performance horses in this age range are checked twice yearly. If you are "asking a lot from your horse" (racing, jumping, barrels, etc....) many competitive riders notice subtle changes in their horse's performance and behavior when there horse begins to develop sharp "points." Geriatric horses with dental disease and abnormal wear issues I normally like to check 2-4 times per year