Google is changing the promotion process such that managers have much more power (for all promotions up to level 5 == senior swe). Previously it used to be, as Michael says, very much in the hands of the committee members who never heard about you or even your team. Now the committee will be composed of your manager and some other two managers from a related team. The committee will not see your own promotion rationa…
my co is moving from managers to anon committee, because it gives managers too much unchecked power to favor/punish. the wheel goes round.
The point being, it's much easier for me to manage the relationship with my manager than with some anonymous committee that doesn't even know me. The manager is already important enough that I would not keep him if he seemed more interested in personal agendas than his subordinates.