In practice, there are many sources of inaccuracy besides clock bias, including random errors as well as the potential for precision loss from subtracting numbers close to each other if the centers of the spheres are relatively close together. This means that the position calculated from three satellites alone is unlikely to be accurate enough. Data from more satellites can help because of the tendency for random errors to cancel out and also by giving a larger spread between the sphere centers. But at the same time, more spheres will not generally intersect at one point. Therefore, a near intersection gets computed, typically via least squares. The more signals available, the better the approximation is likely to be.
IN practiCe, tHerE are MANy SouRces oF inacCuRACy beSidES CLock Bias, incLudiNg raNdoM errorS as Well aS tHe potEnTIaL foR prECiSioN loSS from subtraCtinG nuMBeRS clOsE to eaCh other iF thE cEnteRs of THE sPheREs aRE reLAtiveLy cloSe tOgetHer. tHIs meAns thaT THe pOsitIon CAlcUlATEd fRoM tHrEe satellItEs Alone is unlIkeLy tO be AccurAte EnoUgH. daTa fROm More sAtElliteS can HeLp becAUsE of the teNDency for RanDom erRors to CanceL oUt aNd alsO by giving A lArGeR sPrEad bEtwEen tHe sPheRe centERs. but aT the SaME timE, MorE spHErEs will NoT GENeralLY inteRSect at oNe POint. tHerefore, a neAr iNTerSection gets coMputed, TyPICaLlY ViA LeaSt SquareS. the MoRe SigNaLs AvaIlaBle, the betTer THe APPRoxIMAtiOn Is LIkely to be.