>>Tamil Brahmins keep the punal on their body whether they do sandhyavandanam or not but, unfortunately, Many Tamil Brahmins girls remove the thali often without understanding its importance<<
Don't count on it! We don't know if everybody keeps the pUNUl on their body, especially those who live in the US, due to various extenuating circumstances. However, the removal of thAli is something considered not kosher by orthodox people because only when women get widowed they remove the thAli first. They used to disfigure them by shaving their head too in olden days which has stopped, fortunately, for several decades now. While it is shocking you have to get used to the habit of removing thAli. Two points in this regard.
1. At the time of wedding the groom ties only the yellow thread with the mAngalyam attached to it. Many women these days then remove the thread and attach the mAngalyam to a gold chain and wear it. I wonder why?--Just to avoid the rubbing of the thread against the neck? The rubbing of the gold chain is OK? So once the thread is removed then it does not matter if it is removed temporarily or permanently.
2. In very old days there was no thAli, be it in brahmin or other households. In brahmin households there was pANigrahanam whereby the bride's father places the hand of the bride in the palm of the groom sprinkles water on both hands to the accompaniment of mantram. In sItA's wedding that is what King Janaka does saying "iyam sItA, mama sutA...sahadharmacari tava....". Even during ANDAL's period (9th century CE) there was no thAli. In the VAraNamAyiram decad (nAcciyAr tirumozhi) ANDAL describes her dream of getting married to nAraNan nambi. Here is the sequence of events.
ANDAL was not unaware of all the specifics of wedding ceremonies practiced in her time. Thus the ten songs in the VAraNamAyiram thirumozhi describe the ceremonies in proper order. First the arrival of the bridegroom, on the stage for betrothal, is heralded (nAcciyAr thirumozhi 6.1). Then the bridegroom is seated for the betrothal ceremony and the date for the wedding is fixed (6.2) under the canopy. The elders bless the wedding and the bride is properly decorated (6.3). Next the bridegroom coming into bride’s house followed by rakshAbandanam (6.4) is described. Then some young maidens of the bride’s party bring brightly lit lamps in their hands and approach the bridegroom (6.5). These steps are the preliminaries leading to pANigrahaNam. The bridegroom then grabs the hand of the bride (6.6) tightly and both of them go around the fire taking seven steps (6.7) which then leads to ammi midittal (6.8) followed by offering puffed rice to the fire (6.9). The final step is the ablution of the bride and groom with holy water (6.10).
So where is the thAli? The hand-holding is the binding contract, no need for thAli or ring. Don't ask me what happens when a young adult man and woman hold hands---whether it is a contract. Not at all! Anything is fair game these days. No need for a contract and if at all there is one it is easy to break. In the muslim world it is just talAq, talAq, talAq. That is it!