It doesn't sound like a tough question but surprises me how often it's discussed. Refinishing hardwood floors depends largely on what each person conceives as needing to be refinished, refreshed, or brought back to a new or improved appearance. While some can live with the everyday wear and tear, others may demand the new flawless appearance.
A Few Questions Heard Over The Years.
Q- Can refinishing floors too many times have an effect on the durability or strength of the overall floor?
Not true unless you have an unusually thin hardwood floor that was considered a top nailed floor (photo example right and below). These types were common after World War II when hardwood 
flooring was in short supply. They had no tongue and groove and were nailed into the joist system showing a familiar pattern across the floor. Often these floors are quite noisy as well because the fasteners have lost their grip over the years. Depending on where you live some are still being installed today.
flooring was in short supply. They had no tongue and groove and were nailed into the joist system showing a familiar pattern across the floor. Often these floors are quite noisy as well because the fasteners have lost their grip over the years. Depending on where you live some are still being installed today.Q- Why Don't Some People Just Leave Them Alone?
Some prefer not to have any work done on their older hardwood floors to preserve the patina it has gained over the years. You will lose some of the patina from complete refinishing with some of the more photo sensitive species compared to others.
How Many Times Can The Floor Be Refinished?
This depends on the type of floor you have. Much older antique floors can handle multiple 
sanding jobs because there was no tongue and groove system used when the flooring was manufactured. Thicknesses were greater as well. By doing some research into the invention of tongue and groove hardwood floors it appears they became more predominant many years after the initial invention way back in 1822. However the patent wasn't registered until 1850. To play it safe let's assume tongue and groove manufacturing didn't become prevalent until the mainstream use of electricity or in the late 19th century.
sanding jobs because there was no tongue and groove system used when the flooring was manufactured. Thicknesses were greater as well. By doing some research into the invention of tongue and groove hardwood floors it appears they became more predominant many years after the initial invention way back in 1822. However the patent wasn't registered until 1850. To play it safe let's assume tongue and groove manufacturing didn't become prevalent until the mainstream use of electricity or in the late 19th century.Newer Engineered Floors
Engineered flooring first developed by Anderson Hardwood will have limitations in how often they can be refinished. Cheaper priced floors have the most limitation because of the method in which the floor was manufactured. In other words, there will be a thin veneer on the surface. Once sanded through the layers used to construct begin to show through.
Can The Old Stain Color Be Preserved?
Generally anytime an older floor needs finishing the color and finish is sanded completely off.
