Are you seriously saying you don't know the answer and want one of us to provide it? Okay, but you disappoint me. I thought you knew more.
The Wulff TT is not a long belly line. The head is about 40', most of which is taper. The belly is the thick, nearly-level portion towards the rear of the head and it's quite short. This is a short belly line with a long front taper.
A long front taper is good for delivering light flies delicately and making casts in the "roll cast family". Having the bulk of the mass near the rod tip during these roll casts helps bend the rod easily because the mass sits in the D loop near the tip. Any forward movement of the rod gets the rod bending early and helps produce a good SLP. The taper then allows an efficient transfer of energy from heavy to light line throughout the loop propagation, greatly aiding the turnover of the loop. That taper also means the anchor has less mass than you'd find in a "conventional" line, and since the ratio of the mass of line in the D vs the anchor is important, these lines excel in this field.
The long belly lines with a "negative taper" like Rio Gold IT are much harder to roll cast because there is less mass in the D loop than there is in the anchor. However, they are pretty good for long overhead casts. In my opinion, the main reason for that bulb of mass near the front taper though is revealed in their marketing blurb: "These lines are designed to load modern rods quickly." By having a heavy section near the front of the line, casters feel like they don't need to carry a lot of line to "make the rod load" and they get the sensation of feeling the rod bend without being able to carry lots of line. (Rio and others also accentuate this by making these lines half to a full line weight heavier, because their customers like that and buy more of them.)
That heavy bulb does help carry heavier flies than they would otherwise do. And whilst Bruce has stated that the reason it's there is to "delay rotation of the loop", I have noted that sometimes on my longest casts, my loop can't get past that hump efficiently. A DT line without that hump doesn't suffer the same fate and the loop reaches the leader more easily when the energy of the cast is nearly exhausted. (A better caster than I would not have the same problems, I'm sure.)
So what happens when a long belly line also has a very long front taper? One example of such a line is the Snowbee Rollcast ED line, with a 60' head including a 40' front taper. (There are literally dozens of examples in the 2 handed Spey world too.) These lines cast a very long way and the loop easily reaches the end of the line: it's almost impossible to prevent it! The problem with this line is that it does not deliver a large fly to the target efficiently, so I really need to make sure I fish within the limits of the line. The first 30' is within AFTMA spec on the 6wt line, and since I'm still in taper at that point, the full head really bogs down the HT6 on a distance cast. It feels heavy (of course) but 120' casts are a breeze. It's built for spey and roll casting though, and this is where the line really sings. An 85' dynamic roll cast is a piece of cake.
I find the Rio SH Spey lines to be a pretty good compromise for fishing. Typically from Rio, they are a bit heavier than the standard, but the line is a brilliant fishing line. It obviously roll casts very well, but it can deliver a weighty fly if required or a light fly delicately. The caster can choose how that's done with loop control. The head is a miserly 34', which disappoints me. Maybe they'll make a line with a longer head for us one day.
To summarise: A long belly promotes long carry and long casts. A long front taper promotes easy turnover of the loop, which is perfect for roll casting and delicate presentation.
I still haven't read that Trident article. I hope what I've written above has demystified the differences between the two line profiles for you.
Can you please now answer the question of how you use line velocity profiles when you're fishing or teaching?