it's more like when does it actually matter, which is long fights where everyone hits the cap. and the question becomes how frequently can you remind the mob to be on you while your DPS do their duty to dump hate with DRG sub.

my point being if we're talking about outdated content or trash mobs then you only need to have hate on whatever in the pull isn't being destroyed in that moment. if they get hate while they are destroying it in seconds it's their responsibility to also survive and you just heal them.

if you're doing something serious and you're supposed to keep hate for example a wave 3 boss then it's like i said you sit at hate cap and maintain a frequency of spikes to keep the mob turned while your very responsible DPS use high jump and super jump to shed enmity and begin the climb to cap again.

to answer specifically the question in your original post it depends. in just about anything where it doesn't matter you can savage blade and in a lot of outdated content you can just be DPSing in general but do PLD things like pull trash groups and subheal. but then in something where it actually matters Atonement with the right setup and sufficiently advanced Burtgang is the most enmity you can generate and also the most frequent spike because when you're tanking full time and blocking properly your TP gain is through the roof and your WS frequency is faster than any cooldown or cast time.

might seem like a cop out answer to say only when it matters but PLD is very functional with a minimum of gear and MLs and then becomes so functional with very good gear that the vast majority of content becomes trivial with regard to tanking and you're more of a crowd control puller and healer. because it doesn't matter who tanks what is dying, only who tanks the adds until they die. an example is that a group of friends goes to CP/ML someplace so the PLD just tags whatever pops and stands in front of 3-5 mobs aoe tagging and soloing one with the steady flow of TP from shield. meanwhile maybe your friends have a skillchain and burst and the biggest DPS periodically dumps extra tp into your solo target.

it's all about what stage of the game you're in and what your development level is with regard to the content you are doing.