7.5% Expertise has a little more meaning than let's say 6%, or 8%, or 10%, for simple reasons.
1* It allows you to not get dodged anymore, but your attacks will still have 7.5% chance to be parried on a lvl-93 mob.
While off-tanking, thus, you can simply go behind the boss and hit him from there, and prevent him from parrying any of your attacks even though you only have 7.5% expertise. This is very helpful on many fights (if you can't/don't want to go for the hard cap), since there's a lot of boss swapping going on.
It allows you to build up Rage in a reliable way, before you have to taunt off the boss, and also prevent any DPS loss you might have due to Parries (very roughly ~7.5%), even though you are not hard-capped.
2* On Ultraxion/Spine tendon type fights (agreed there aren't that many out there, but still) there's simply no point in going for a hard expertise cap, since those mobs simply can't parry attacks.
3* Agreed that since MoP this ''magic number'' has lost a bit of its charm (it was even 6.5% before, as a reminder), since in previous expansions it used to remove both all your dodged attacks and some of your parried ones, and the Hard cap only allowed to removed the rest of your parried ones.
But even so, for the reasons stated above, there's still a lot of meaning to ''soft cap'' at 7.5% expertise, if for some reasons you can't go for the hard cap -- be it for your gear lvl, the fight mechanics, your personal preference/game style, etc...
All in all, in my humble opinion (as there's no maths to back this...), yes, it doesn't have the same magic it used to have, but there's nonetheless still a lot of sense to go for that soft cap in some few situations.