Hi there, I've run a one-(wo)man corp several times for many years. Sometimes it just works for your character.
There's always a balance between "time investment" on one hand and "in-game" representation on the other.
For a character that has to be in-charge of their own destinies, being under someone else's thumb is sometimes not an option. When there was time years ago to run a large group of players and an alliance, I did those things, when there wasn't time, I stayed in a one-man corp to still be 'in charge.' I've made sure to have Silas always be the CEO of whatever corporation she's in in the entire duration of her Eve life, sticking to those IC guns.
I took no small amount of constant ooc grief from my alliance mates being the one corporation in the alliance with a single-member. But gotta be that way
I think as has been stated elsewhere, the difficulty for RPers is maintaining a group story with many moving parts. With a one man corp you control the message and the actions and the 'story.'
When you add others you lose control of the IC message unless you are strict with the pvp/igs/and public image.
RPers don't seem to give a shit these days, but in the old days Rules of Engagement were a BIG DEAL to RPers. This was before FW, but say when an Amarr FW group gets a negative concord rating and is GCCing, that used to be cause for public ridicule and PR issues with the law abiding types. Having a large group meant you had to be ON TOP of all your people and who they were shooting, as other RPers would track this stuff and make a stink about it (rightly so), so when group A says they are 'anti pirate' and half their members are blowing up freighters, they got called on it.
I don't think this is as much of an issue as it used to be though.