At my TWR, in the small local airport, I often give landing clearance when pilots report "inbound on final"(about 12 DME), the rest of working from then belongs to him, my working just observe RWY and preparing for "go around" clearance in any abnormal situation; why we have to wait until he is too near the RWY? Infact pilots always request landing clearance on short final if I have not given him yet on long final. My work is non radar app, using VOR/DME.