No daily stand-ups, no wait for code-reviews, no feeling alone.
One person controls the keyboard (typist), the rest of mob think and guides.
Make rotation periods (maybe 10 minutes), your turn as typist provides you mental relaxation because you can just obey.
Small teams (3 or 4 people) provides the best benefit-cost. In big teams the speak time of one person shrinks because everybody want to speak.
Group decision are superior over individual.
Continuous and implicit code reviews (no wait, no long lived branches and no context switches).
Rewarding flow: we never fell blocked by ourselves, it feels great.
Sharing knowledge: Misunderstoods, forgetfulness and mistakes can occur, but when mobbing this is detected instantly. The cost of a person's lack of knowledge is often very high and is never accounted for.
Get the best of your team: everybody has good and bad skills, mob makes you match and use your high points.
QA people need to be an active voice The process of development should be guided by tests on story and acceptance criteria