First of all, the Rebbe said that they should not take pictures together and especially not at any photo shop either.

Secondly, the Rebbe objected to an engaged Chossan and Kallah even flying on the same plane together – to the extent that because of it the Rebbe refused to be the mesader kiddushin at their wedding despite their claim to the Rebbe that they didn’t know it was unacceptable.

Thirdly, the Rebbe opposed any meeting between them altogether.
Despite the story when Rabbi Leible Groner was a chooson where the Rebbe told him that he could meet not more than once a week – that was back then in 1954 when the situation was half normal and people were more decent. However, already in 1962 apparently when the Rebbe saw what was happening with all the hefkerus and breeches in tznius/yichud by engaged couples the Rebbe took off all the customary wedding date restrictions of not getting married the second half of every month, (except Adar,Elul & Kislev where the whole month was mazaldik) Lag Ba’omer, shloshes yemey hagbala before Shavuos – and said that it’s not proper for Jews and especially not for chossidim to meet before the wedding; they should concise the time in between as much as possible and just get married asap.
See the Rebbe’s letter printed in Shaarey Halacha uminhog chelek daled page 92

Holding just before purim here is another story furthering the issue.

Reb Yeshaya Hertzel relates:
As a choson, I was aware of the Rebbe’s
directive not to meet the kallah during
the engagement period, so we never met. However, when Purim came, my family managed to convince me that it’s alright if she joins us in a family setting for the seudah, since she will sit at a separate table. Since I conceded regarding Purim, as Pesach approached I was pressured again to have my kallah come for a yom tov meal. I wrote in to the Rebbe asking what to do, and received the following response: “Al
horishonim onu mitzta’arim vechulu v’ata ba l’hosif aleihen?!” [“We are still pained over the earlier ones, and now you want to add to them” – Rashi on Shemos 18:2], meaning that the Rebbe was still pained from the Purim incident, and it was obviously out of
the question.
(Bakodesh Chazisicha, page 85)

I think having it taught properly would be very valuable. I would say that personally my “sensitivity” is higher than average, but I can’t say I was ever taught any clear guidelines about these things. It’s important to explain our values clearly to the next generation.