In a stock 1959 or 2203, V2b is wired as a cathode follower (CF). Its job: present a low-impedance source to the tone stack, which is itself an inefficient passive network that loads the previous stage heavily. Without a CF, the tone-stack components would dominate the mid frequencies and you'd lose snap.
Two Jose-canonical mods interact with the CF:
1. The Jose Master Volume sits between the CF output and the tone stack. This works because the CF can drive even a 1MΩ pot without significant droop — a regular plate-loaded triode would compress noticeably under that load. (Try putting a 250kΩ MV here and the CF starts to compress *more* noticeably — possibly a feature, possibly a bug, depending on taste.)
2. The "4th gain stage via tone-stack relocation" Tier 2 mod repurposes the CF. If you move the tone stack to V2 plate (so V2 plate drives the tone stack directly), the CF triode becomes free to be wired as another standard gain stage. This is what the Tier 2 mod does — turning a 3-stage preamp into a 4-stage preamp.
Note: cathode followers can clip too, asymmetrically and ugly. Hot-rod builds sometimes underbias the CF on purpose to produce a particular kind of grunge. Jose tends not to do this — his canonical CF is biased clean.