Long ago, above ground pool main drains made sense, before the large filter systems and automatic pool cleaners. The extra circulation the drain offered helped the smaller systems turn the water over. They were also beneficial in keeping the pool cleaner as the dirt could be brushed towards the center and drawn into the drain.
Today's filter systems have no problem turning over the water in a reasonable amount of time. Automatic pool cleaners help in this regard also, drawing water from the bottom of the pool.
An automatic pool cleaner is a much better cleaning solution than cutting a large hole in the liner of your pool. Main drain leaks are very hard to detect, and left alone, can cause considerable water loss.
Vinyl pools can start leaking for any number of reasons. In most cases it is small holes around the outer edge of the pool. It is also possible to have pin holes across the bottom of the pool. Cleaners spending too much time in one spot can cause these. Skimmers and returns can also leak if the screws are not tightened periodically.
Holes in vinyl liners can be from many different causes, there is no reason to add one more possibility, one that is almost impossible to detect.
When properly installed the drain is seldom the cause of leaks, but I have always been amazed at how every one with a drain is sure that is the cause of their water loss. This is seldom the case, but it is the one spot that is next to impossible to do anything about.
If you are going to add an extra hole in your liner it should be for an additional return. Large filter systems perform better with two return flows. At least this type of opening is easy to detect a leak in, as opposed to a bottom drain.
Those are my reasons for not installing a center drain but you will find many people who would not consider owning a pool without one. If you are going to do it you might as well do it right. It is now highly recommended that two drains get installed instead of just one. In some places you will find this written into the building codes.
Here is what a dual drain setup looks like and this kit would provide you with everything needed for the installation.
Learn more about automatic pool cleaners and why the Lady Bug is my personal favorite.
For more above ground pool questions and answers visit these pages