By installing a drainage system around the inside of the basement along the wall, you can capture water at the most common point of entry - the floor/wall joint. You can also capture water from the walls and prevent the center of the basement floor from leaking by intercepting the water at the perimeter of the floor before it gets to the center.
The advantages of an interior drainage system include:
1. Accessibility to do the job.
2. More affordable than an outside system.
3. Installs in a day or two.
4. Easily serviceable year round.
5. It works.
Even in basements that are already finished, it's still much easier to waterproof from the inside than the outside. Most full-time basement waterproofing companies offer interior drainage systems - between which there are big differences in systems. Some are old-fashioned and generic, and others are modern and specially designed for the job.