Due to many reasons, such as aging, weathering, wearing..., some concrete floors appear to be soft. When prepping such hardness of floors, the proper diamond grinding tools to be used are important. The application of improper diamond tools cause inevitably inefficiency of work and significant loss of tool life. Generally speaking, you need to use hard or extra bond of diamond segments in order to work efficiently and correctly.
Heavier machine grinding the floor down more, when you you lighter weight of grinders, you need to think whether or not you need to add extra weights.
Lower grits of diamond segments are usually applied for initial floor preparation. But all depend on how deep you plan to cut down and after finishes you expect to reach.