#1: Your perspective - the toes are the farthest part of your body from your face as you can get! You may think you 'got it all' but could find out a week or so later that something's still festering.
#2: Risk of infection - all it takes is one mis-clipping and the skin's natural bacteria can grow out of proportion and cause an infection. This infection can become a very serious problem fast. Instruments you may be using at home are not sterile.
#3: Risk of bleeding - in some cases, ingrown nails treated by people who are on blood thinners can start to bleed and be very difficult to stop. You may end up in the office after all, so best to keep it simple and leave this one to the professionals!
#4: It may be something else - there are some conditions that present as feeling like an ingrown nail, but when it isn't an ingrown nail it could be a serious vascular problem (poor circulation) or something simple that doesn't need to be messed with (a callus on the corner of the nail).