I find that there are some situations where I am not sure whether the other person enjoys my presence enough to warrant further interaction. For example, if you meet someone during a talk at the end of a conference, talk with them for 5-10 minutes, and then get up to leave, do you wait for them and walk out with them or would they wonder why you want to walk out with them if you just met? Or if some people you met at the conference walk in line behind you while at the airport, is it acceptable to join in on their conversation? Or if some people that you just met are talking about going out with some people that they know a bit better and you're standing there awkwardly, is it acceptable to ask if you can tag along?
I fear that in these situations, if I do act, then they may think something along the lines of "I barely know this guy, why is he (any of the above or similar actions)?" Most people will say yes to be nice the first couple times, but I don't want to be with/inconvenience them if they'll be thinking the above text.