Anything that’s called an imager is usually to do with stereo in my experience. Yeah it’s really good to understand how stereo sound actually works and what to watch out for with it, definitely worth some time reading up on. Basically an imager lets you reduce or increase the perceived “stereo-ness” of the track you put it on, all the way down to mono if you want (some are multiband, so you can affect different parts of the frequency spectrum differently. The free Ozone Imager on the iZotope site isn’t, but the one that comes with the full licensed Ozone is, kind of confusing cause it’s called the same thing. Anyways…) That said, if I’m making a wide sound fully mono I’ll just use a utility plugin to take one channel (left or right, doesn’t matter which) and isolate that instead.
But put more simply, you can get general weirdness from having your sounds be too wide, or having too many different wide sounds in your mix overall. And anything below ~100-120hz region should be totally mono. Reason being is that for something to sound “stereo”/aka wide in a 2 channel stereo system, it has to be different in one side than the other. Usually that happens by a slight time delay between the two which literally means that with stereo effects (chorus, phasers, stereo delays, reverbs) the sound coming out of the two channels is out of phase (basically, the two channels are in different points in the waveform) which carries inherent problems with it (phase cancellation, basically like putting a comb filter onto the sound. Dips a bunch of notches out of the frequency spectrum). Not to say you shouldn’t make sounds stereo obviously, just have to have to manage the issues that come along with that. So that’s mainly what you’d use it for. That said what I’ve heard of your tracks it hasn’t sounded like you have major issues with that
And Haas effect refers to using a delay to separate the left and right channels by a few milliseconds (say about 10-20) to make the sound wide. Choruses do that in combination with some pitch modulation and things like that, but you can do it with a basic delay by just turning the feedback to zero and setting both sides to a very short time, but slightly off from one another by about the amount mentioned (say, 1ms left, 11ms right. Doesn’t have to be exact). Good for sounds in your track that you want to have that width and aren’t central elements. If you do it directly on drums, sub bass, leads and other things that need to be really central and present in your mix, you will have phase cancellation issues. But you can mitigate it afterward, when appropriate, if you want the sound to have width but be less wide than it is by using an imager. Wouldn’t go to that though if a better solution is to just remove the stereo effects in the first place, or put them as a send so you maintain the original signal separately. Hope that all made sense 