Sometimes I do, at other times I don't and I don't sweat over it as excuse ' it was so many people when we met " seems to be working. On another hand, to be even handed , I don't take slightest offense if people I met before forget my name, I use the same excuse above as showing I don't mind.
As for bringing Instagram or any other social media into it, I wouldn't at all. I'm reluctant to share contact information with people I met for the first time, simple reason being , often I would be thinking ' who the hell that person is".
Of course when travelling, different , more relaxed rule applies as it's handy to have contact with other travellers , not to mention guys in the business.