I've been working on my level this week, and started getting a message every time I save it (which is really frequent):
"Woah! This level is getting really complicated, huh? With all this stuff going on it might make it difficult to publish. You might want to try getting rid of a few bits and bobs if you want to share your creation."

The thermo's only about half full, and the level's a long way from being done.
It didn't start until I added a sackbot to handle a spoken intro. Relatively speaking, the sackbot's not that complicated. There are some magic mouths on sequencers, and some rudimentary follow waypoint behaviors. There's no acting or elaborate character animation.

With all the problems I've heard about, I'm not going to use a dynamic thermometer. The various sections don't really work that way, anyway. They come to the player, not the other way around, so that would just make it more complicated than it needs to be.

I can work out something other than the sackbot if that's the problem, but everything else is just going to get bigger. I haven't even started decorating yet.

Is this something I should be worried about?

(edit: I captured the sackbot into my objects and removed it from the level, and the message stopped. That's frustrating.)

My only suggestion is to build the level as you normally would and see if it publishes fine. The message could also be the result of a glitch, because with a 50% filled thermometer, you shouldn't be getting an error like that. Try copying the level on your moon and deleting the Sackbot from the copy, then saving it to see if the error shows up again. The game might just be trying to warn you that too much recorded dialogue could cause the level to take a long time to load.

I totally agree with Fox, I have the same message, every time I close the editor, I think that its a kind of warning to "remember" creators not to use too many different objects and materials! Nothing more! But I haven't published a level in LBP3, so maybe I'm wrong! I would be worried not before you get lots of red or yellow exclamation marks. Have a lot of fun creating and many greetings, Jürgen^^

it's just.. an annoyance really. I wouldn't worry about the warning itself. but the thermo is another story. if it's too high, others will have an issue joining another player in the level (and will most likely separate a group trying to play).

you mentioned not using the dynamic thermo. I think that's probably best for now if you can avoid using it.

If the thermometer is becoming a big issue you can always use the good old emit-destroy system. You would need huge amounts of logic inside a sackbot for a message like that to appear. As other here said, it can just be a glitch. I would copy everything in the level and use them in a new empty crater on your moon.

the thermo's only at about 50% (a bit above now that I've added pieces). It's an infinite side-scroller that uses a few dozen emitters to drop in the various sections, which are then destroyed after they leave the area of play. I'm keeping a copy of each section staged in the level (out of sight) for the emitters to reference. I'm not worried about the thermo getting too high, it was just that message that appeared after adding a sackbot kind of shook me up.
I'm going to leave the sackbot out until the very end, and if there's not enough room at that point, that will just be too bad. The other parts are much more important. (I'm actually starting to question whether an intro is needed at all. I got a funny little script written, including the sackbot getting mad if you skip it, but it's really not important to the level.)

Don't forget to use the dephysicalization tool or whatever its called (the tool that takes away collision detection) on objects that the player doesn't physically touch. That includes scenery and other stuff. By taking the physics away from objects that don't require it, you're lessening the load on the level. You can do the destroyer thing like the other person mentioned, too.

I was planning to dephysicalize some parts just to avoid collisions as moving parts go past each other in opposite directions. Didn't stop to think it could ease the load on the level. That'll help. Thanks.

sometimes that message appears if you put many things very closer, try spacing things.

I've experimented with dephysicalization. it honestly doesn't seem to really change thermo or anything else really. but yea.. if you're at 50% thermo then you don't have anything to worry about. LBP3 is more sensitive to this than LBP2 was. seriously though, I got the warning just from pulling out one of my long songs and opening it. it would probably give that message if you just looked at it funny