Short answer
They do different jobs, and how much of a party's audience the leader carries varies hugely. In British general elections the party page was the campaign machine and the leader's page was the personal voice. Across 2010 to 2020, some leaders drew most of their party's Facebook engagement and others drew a quarter or less.
What the evidence shows
- In 1,208 hand-coded posts from 2015 and 2017, party pages were far more likely to ask people to share (59% against 8%) and to vote (55% against 35%). Leader pages used more first-person language (53% against 32%) and more personal messages (14% against 4%).
- Leaders' share of their party's engagement ranged from 79% for Nigel Farage at the Brexit Party, 75% for Leanne Wood, 74% for Jeremy Corbyn and 71% for David Cameron, to a quarter or less for most Liberal Democrat and Green leaders.
- Leader pages added nothing to the party page as a signal of polling, and in periods when more engagement went to the leader, the party polled lower: by 0.7 points for every 10 points of leader share.
- Election campaigns lowered the leader's share by about 6 points, because party pages doubled their output.
Caveats
The link between leader-centred engagement and weaker polling is slow-moving and depends heavily on Labour under Corbyn and the Brexit Party. It is an association, not proof that leader-centred campaigning causes lower support.