Getting hurt twice takes a bit of time and requires adding awkward extra stuff at the beginning of the level. And say I want to play through a campaign that someone else made, but I think it's a bit too easy, so I want to try it with only 3 health on each level. Either I can use a hex editor to remove all the passwords, go through one by one adding some extra hurt events, then wait a few seconds at the start of each level before I could even play because I was busy being hurt. Or, I could press "t/smhealth 3" and play. Also, the hurt method doesn't change the maxhealth. So if a full NRG is placed anywhere on the level, it will negate all the work I put into adding hurts. Unless I'm supposed to hunt down every carrot before I even try running the game.

For more complicated triggers, like background stuff or foreground stuff through reworder, I might want to figure out if the trigger works before I even decide on a location for the crate. Also, crates are generally placed in difficult to reach places on purpose in single player. For testing purposes, I will cheat to get the crate, because it can be a huge waste of time running back and forth in sections of the level I've already tested just to get a crate. JJflyjjnowallsjjinv, flying there, jjflyjjfly, stomping the crate, jjfly, flying back, jjflyjjflyjjnowallsjjinv would work, but "t/trigger 1 on" would be faster and more convenient.

JJnext is great when I want to go to the "next" level. Not so much if I want to go to the previous level or something that's not in the set of consecutive levels I'm currently in.

Uploads that require plus will say so. Plus is easy to find, and easy to install. I think refusing to add features that could enhance the experience of many people who play jazz, because the off chance that someone out there may get a bit confused, will prevent more good than bad. I've seen poorly designed uploads on J2O that can easily put a player in a situation where the level is unwinnable, and I realize that it can be annoying. But I think no matter what features plus has, you'll always see more problems from poorly designed regular levels than different gamemodes. And those levels have not discouraged every new player from sticking with JJ2.

I didn't say single player is boring. I said, "...having to stand back and mash the shoot button..." is boring. Single player can be awesome. For example, episode 5 of the Resurgence of Devan by EvilMike was brilliant. It had levels based around moving platforms, lots of horizontal springs, rising and falling water levels, delicate platforms that would crumble if you weren't careful while walking across them, etc. Winning took finesse, not button mashing. The reason a lot of single player stuff is boring is that the gameplay is redundant and simply involves shooting a couple enemies then jumping between a couple platforms. Adding new features in plus would allow for more unique gameplay and would reduce boredom.