When I bought my house it had some water problems in the basement, nothing big, just a bit of water on the floor now and then. I was fairly sure it was just because the yard's grading was poorly done, and there was a sidewalk along the side of the house that sloped towards the foundation. The fact that the rain gutters were broken and filled with dead leaves and sticks of course didn't help anything either. I had already removed the sidewalk and one day, in a heavy rainstorm, I discovered the real issue. The water was puddling where the sidewalk was and actually getting higher than the base of the window and just leaking right in. The obvious solution to this raise the level of the dirt on the side of the house to keep the water from puddling at the windows. This would require bringing the yard higher than the windows to insure the slope would be sufficient to achieve the results I was looking for. I couldn't just shovel dirt halfway up the windows, as that would lead to many problems, so window wells to the rescue.
Window wells form a nice "wall" that keeps the dirt from getting too close to the windows, and enable the windows to be lower than ground height without having to worry about all the water from a rain shower/storm just puddling in the window area. I ended up raising the height of the dirt on the side of the foundation close to eight inches, gradually sloping out about three feet. When it rains now most all of the water flows away from the house where it can soak into the ground and not leak into my basement.
Installing window wells is really easy, dig a hole for the window well to sit in, affix it to the house, I used cement anchors, but you could probably get away with a strong landscape adhesive if you wanted. Once the window will is attached to the house you backfill around it, to create a slope that travels away from the window and put some landscape fabric on the inside and some stones to hold it in place, and keep weeds from growing. You won't be able to run your mower in the well, which is why the landscape fabric is used.
Since installing the window wells, and raising the grade on the side of my house, I've had zero issues with water getting into my basement.
If my house a drain tile and a sump-pump the window wells should technically all lead down to the drain tile, so the water that does get in them can drain to a crock and be pumped out.