Replacing an inner rocker structurally seperates each end of the tub. Beforehand the tub has to be braced exactly in position or the door gaps end up a mess. Replacing one side at a time keeps a reference point as to the correct component overlaps.
As noted, the inner rockers rust from the inside out, usually showing as holes along the bottom. At that point or even before, the integrity of the tub is compromised. It's worth removing the footwell side covers and inspecting the bottom of the A pillar connection to the inner rocker. Rust problems there caused by damp silt build-up over winter is also structural. After a few years it's amazing what hoses out of that cavity. Nowadays with mainly weekend usage, I prefer to leave the covers off so the cavity can be regularly cleaned out, but any speaker cutout has to be sealed so water doesn't get in cabin. Another option is to remove just the bottom of the covers for garden hose access.
By comparison outer rockers are a much simpler to replace, or at least they were when NOS was available with the matching curve to the bottom of the doors.
Viv