More than merely convenient...
Stairs from the garage leading directly to a basement can minimize a lot of problem issues. One of the moist obvious is moving large/bulky items in and out of that lower level. Relying only on an interior staircase may present challenges, particularly if that inside staircase has angles or is "U-shaped" when moving furniture.
Additionally, direct basement access from the garage can be quite handy for home and D-I-Y projects. Your workbench and tools may be located in the garage, in the basement, or in both locations. Certain projects require more room to spread out in.