20 second heavy while on mount, whats the point?

[SummonerSenah]

Longer it takes to get somewhere = more time spent playing = more dollarydoos for SE. (It's stupid though.)

That's not quite accurate. You don't pay by the hour to play FFXIV. The cost of a subscription is the same whether you play for one hour a month or 50 hours. If SE is concerned about keeping people subscribed, it would actually be more effective to get rid of heavy since most people find it annoying.

tl: dr - It's a bad mechanic, period, with no benefit whatsoever.