Cracked and missing grout can detract from the looks of a finished tiled surface. Once you see this happening it could be the first signs of more than just poor grout finishing techniques. Often customers think they can just repair grout when they find it missing or dislodging ,but there can be an underlying issue. When tiles have become delaminated, loose, hollow or drummy there tends to be some movement between the tiles and adhesive. With foot traffic this can cause tiles to move slightly up and down loosening the grout joints. Piece by piece the grout will disappear with every run of the vacuum over the tiled surface leaving the tiles exposed to even more damage. With the slight up and down movement of the loosening tiles there is the chance the grout pieces can work their way under the tiles. When chunks of grout get under the drummy tiles there is a high chance the tiles will break or crack, causing tripping hazards and sharp edges. Once you start having broken and cracked tiles the repair job becomes a little harder as there may not be any spares for replacement. In summary the sooner the loose tiles are repaired with the tile injection system firming up their foundation, the better it is for your tiled floor area.