They have good "playability".
That means, even oop they play pretty well due to flopping the majority of their equity (flush draws, straight draws, 2pr (draw)). It is often very clear whether suited connectors are able to continue or not (unlike Ax type hands, which find themselves in a way-ahead-way-behind-situation more frequently).

Another important thing is "board coverage". If you do not openraise suited connector you won't be able to make money on 257 type flops vs. reasonable opponents because your UTG range does not cover those low cards.
It helps to represent flushes better or straights, which overall will be important when trying to win a hand without nuts.

However, most suited connector should achieve a positive EV by stealing pot pre in combination with flopping/improving to a nutted hand postflop.

In my database they are pretty marginal from UTG. I don t think -ev in my sample but not spectacular. Board coverage and whatnot only really matters vs players who ll take advantage of you not having certain hands. With a solid plan they should be able to flop enough to fight for the pot. With aggressive players IP behind you can drop them.

Preflop, suited connectors have higher expected value vs. premium pairs that have higher equity. Higher equity hands will maintain their strength on dry flops more often than hands with higher expected value. However you have a better chance of making nut type hands with hands that have higher pre flop expected value than hands with higher pre flop equity.

Table dependant and depending on your comfort level I would recommend attempting to start by opening UTG with some of the higher suited connecting hands (QJ, JT, T9). This will help you to get a feel for how these hands can be played OOP post flop before opening with a hand like 54s which can be more challenging but more rewarding than JJ TT on a lot of boards.

Thank you. That makes a lot of sense. I appreciate the help & advice.

Depends on how deep you are as well imo

snowie prefers to open raise K9s from UTG than low suited connector such as 87s. how do you think about?

K9s can have TPGK if it hits 9 and can c/c when king comes on the board. also, it can make 2nd nut flush.
when some high card comes on the board, K is a good blocker, so can c-bet comfortably.

for me, K9s is easier to play on the postflop than 87s.

K9s is a better hand then 87s by a lot equity wise. Domination doesnt happen enough and flopping over(s) and K high FD gives us a lot of playability. Suited kings are underrated imo.