[Cillaz]

turning off all the things mentioned helps reduce the likely hood of lagging/lag spikes. It's not a computer thing, it's a server thing. Depending on how many people in zone and how many actions you are making the server perform (displaying dot damage and further clip planes etc) it can 'lag you out'
You'll still see enemies following you, an you'll still be running around etc, but you won't see any Songs landing, or songs casting (they will gray out and you won't be able to recast) an you won't be able to type etc. Then eventually you will disconnect. It can seem like you're still playing, you won't see any change on your m/s connection bar or anything so the first few times it happens it can take a while to figure out what's happening.
It's a server side problem and varies from zone to zone depending on amounts of people in zone etc. I have had a train of 20 in loio when there were 35ish ppl in zone and lagged out, only to log back in, move to FV and pull every mob I can see (80+) with only 2 others in zone and be able to swarm normally.
Also had small trains in FV as lots of players in zone, get lagged out, come back later when less in zone and can then swarm a massive train.

Long story short, the turning off of lots of things is to reduce the likely hood of lagging, as even with a good comp and connection it can happen