Great tips guys! Keep them coming, ill write some more of my own every few days as well. I'm surprised echo has any lectures up, they usually take them off a few days after exams finish. You guys got lucky to have any up at this stage :p.
I'd echo the safety and legal thing. It's not just that though, sometimes theaters are packed to capacity, if you have people coming, they push out the people who are meant to be there and it makes the experience worse. One year there were two biology spots, an early one and a really choice one. I was luckily enough to be allocated to the choice one but lots of other people who weren't enrolled in it showed up. It made it very hard to get a seat and people often sat in the aisles. Not to mention it makes it harder to ask a question/takes up more of the lecturers time. I guess its also the principal of the thing too. If everyone acted in that way (showing up to lectures theyre not enrolled in) the entire thing would just break apart. You can only act in that way cause most other people don't (granted its mainly because they cant be fucked/don't want to). That said, it usually empties out a few weeks in for almost all subjects and theres definitely no harm in going to these i guess (but you could always just stream them too).