For an FMS-based approach using LNAV and VNAV, the data is already relevant there. But there are different ways to fly an approach. ILS, LOC, RNAV, VOR, NDB. ILS uses signals from ground transmitters, which guide the aircraft laterally and vertically when APPR mode is activated. Will or may one use only the signal of the LOC, only the mode LOC is activated. VOR and NDB Approaches can be flown using RAW data (reception of the NDB or VOR), but the autopilot can not take off signals automatically, so you have to control via HDG (or by hand). Also there is no vertical guidance here, but one must sink again, this time however also with the help of the autopilot (VS). In today's times, however, for these approaches, as well as for the RNAV approaches, the data in the FMS can be used to ultimately fly to check all data using LNAV and VNAV (in VOR and NDB but in parallel under control of RAW data). In some aircraft, the LNAV and VNAV modes are also flyable as an IAN as an ILS approach. But the 757 does not offer that. On the approach using LOC, ILS, LNAV and VNAV, one approaches the IF on a fixed routing or vectoring, then activates LOC, APPR or LNAV. When APPR is then automatically captured the GS, at LOC, VOR, NDB or RNAV, the descent is then started by means of VS or just VNAV (previously adjust the height accordingly and check the data on the LEGS side). That's a quick answer