There are three certainties in life: death, taxes, and concrete will eventually crack.
If you discover a crack in your basement floor, wall, or foundation and it is not leaking, should you fix it? Well, you know the three certainties in life, but there is another: a foundation crack is going to leak sooner or later, you just don't know when. There is a reason people repair foundation cracks. One, because you get the cold air coming through. That is like having a football sized hole in your foundation. You can imagine how much cold air can come through that. You can also get radon and moist air coming through, creating a problem with mold. There is also organic material in the soil that is breaking down and creating odors which can come in from foundation cracks.
Besides that, wood boring insects can come in and, if the hole is big enough, snakes can get in from cracks in a foundation too.
Another big issue is when people are selling their home with a foundation crack. The average person thinks that means the home is going to fall down, when in fact it's not. But, you have to work with the mind of the buyer and you also want a bigger pool of buyers. If you have a foundation crack that has a warranty, it makes the potential buyer a lot more comfortable.
Additionally, if an appraiser comes in they are usually after the home inspection. If the home inspector comes in, sees the crack, and tells the buyer about the crack, they may interpret it as a big deal. They may want thousands of dollar off the price of the home, when it is only hundreds to fix.
If the appraiser sees it, and it is an FHA or VA loan, and the crack is put on the report, they will want a structural engineer to come in. We know most cracks are not structural. It saves a lot of hassle and aggravation for all parties if a foundation crack is repaired prior to listing the property.