Suited connectors like 67, 56, 45, 34, and even 23 won't have positive EV in most of the situations. When should you consider entering the pot with these hands and feel better about it?

These types of starting hands can have value if you are holding a late position (Button or Cut Off) and there is already a small raise and at least one call before it's your turn to act. You need to make sure that everyone is playing fairly deep so if you manage to make a flush, straight, trips, or two pairs then you will be able to get value for your hand on betting many streets.

Having a position to act last will also add value for bluffing if the situation allows that kind of play. Blind vs blind these low suited connectors have obvious value, and when facing a small open raise, you will have nice +EV to call from the big blind and see the flop with these hands.