Tucking helps open neuro-kinetic flow and mindful re-tucking keeps it open.
We tuck to protect our lower back and if you are puzzled why you may not be
sweating, it's a clue that your tucks may need more attention. Tucking and
tightening the gluteal muscles are not the same thing. As we scoop the
lowest part of the pelvis forward our muscles do tighten somewhat. But
make sure you scoop first, then tighten buns AND mentally push those
lower abs inward for a correct and stronger tuck.  Progress to deeper knee
bend in order to attain a better butt tuck which will allow better shoulder to
hip linear alignment. If you don't tuck, you could add inches to your waist
and hips. There are different degrees of intensity to tucking. Try it in the
T-Tapp stance during your day when you brush your teeth or in front of the
kitchen sink. See how good you can do it.

Experienced T-Tappers learn to retuck several times during each move. It's
because we lose our tucks  a second after we do it. Think how many times
Teresa tells us to tuck in a single move. Make it a game to re-tuck each time
she says the word.

Lunges start with proper set up. If you can't tuck at all in a lunge position,
move your feet a little closer together. And in the first set of lunges, bend
knee toward little toe first, then tuck the butt second. You might want to try
this; re-tuck each time you go down, and each  time you go up. Pay special
attention, and it will  make you realize you weren't holding the tuck.

In other T-Tapp moves, the tuck comes first, then knee to little toe.

Reminder during
plies: strong tuck throughout! Most of us set up correctly,
then when we get to the shoulder alignment the butt goes back out. And on
the up and down, it's not how far down you go, it's more important to keep
the tuck, keep the hip to shoulder alignment perfect, and to push those
knees toward the wall behind you and do not relax the contraction in the
thighs at all.

When arms are straight above the head in all moves what do you do even
harder? TUCK and squeeze the butt! Remember this in Step Away the
Inches and on the floor as well.

In
flat back moves(like PBS, pull the weeds, the box.) your butt is arched to
the ceiling and the butt and abdominal muscles are held tight.

On one legged moves (Balance, TTN, HD) really bend that standing leg
deeply so that you can get a better butt tuck, and only go as high as you can
WITHOUT losing the butt tuck and when you reach those peaks (at the front
and side with your knee) tucker HARDER. The combination of pushing the
knee back and up with tucking will trim the abs like nothing else.

Just always go to your max and you'll continue to progress...layer by layer.
The Butt Tuck