My wife and I invested in a zippered mattress cover about 10 years ago when we bought our current bed. We did so because we were led to believe by the salesperson that it would really save us a lot of money and aggravation in the coming years. I was skeptical, but the cover was not that expensive, so I went ahead and bought one. Now I am very happy that I did, because I have seen how having a zippered mattress cover has really benefited us.
One of the biggest problems with mattresses is that they eventually become very heavy. They do this because of skin flakes, perspiration, dust mites or whatever else they fill up with. With a zippered mattress cover, you can pretty much avoid these types of problems, because it is specifically designed to keep out such nuisances and allow your mattress to stay light and clean. For anyone who has ever had to throw out a mattress that has been slept on for a decade or so without a cover, it is not a pretty sight!
Another thing that a zippered mattress cover does is prevent any type of staining from occurring on the mattresses. I am one that likes to surprise my wife with breakfast in bed from time to time, and invariably something gets spilled. With a zippered mattress cover, we do not have to worry, because we know that nothing is getting through that cover and that the mattress below is safe and sound. For me, personally, I would much rather wash some sheets than try to figure out how to clean a mattress stain.
I have noticed another benefit of the zippered mattress cover, that it seems to cut down on static electricity build-up that occurs when the mattress and box spring rub together. I remember before using the mattress cover how I would sometimes get a serious shock from trying to turn the mattress or move the bed. Now, I might get a tiny zap, but it is nothing compared to the way it used to be, where I would actually have to wear work gloves while moving my mattress because I would get jolted otherwise.
A zippered mattress cover has a number of benefits that one may not expect. I have bought one for every mattress in the house at this point and would not have a bed without one. It has dramatically lengthened the lives of our mattresses and kept them in pretty good shape. It may not work the same for everyone, but for us, it was a great investment!