There are certain events which grant XP to only a single character rather than the whole party.
For example some events during the initial trip on Lady Vengeance after Fort Joy but before Reaper's Coast and the Three Altars quest on Reaper's Coast.
If the main character happens to be the lone beneficiary of the XP, there is a workaround ? exploit to get the other 3 characters to gain the XP as well.
This is by dismissing the whole party and then recruiting them again, which automatically bumps them to the main character's XP level (as it is higher than the henchman's XP).
As a result, awarding XP to a lone character seems rather pointless with this workaround
