Basically, if I am going to edit a photo further outside of Lightroom, I will export a tiff. Otherwise, it goes out as jpeg. Like, say I needed to do some touchup work with the healing brush or whatever in Photoshop, I’ll save a tiff out of Lightroom and then work on it in Photoshop. The ONLY reason for this is that tiffs are lossless…even if they are compressed, information does not get discarded from the image when you save your edits.
On the other hand, a jpeg is LOSSY. Every time you save, the jpeg engine in the software you are using analyzes the image according to how the human eye perceives color, contrast, etc., and then discards some information from the file in order to save space. If you edit, then save a jpeg a whole bunch of times, each time it’s discarding information, and each time you save, your image quality goes down.
That said, if you are finished making edits to the file, either in LR or PS, just export as a jpeg. It will look the same to your eye, and the file with be orders of magnitude smaller (as you figured out…)
So, my standard workflow is either:
lightroom -> jpeg (if I’m not making edits outside of lightroom), or
lightroom -> tiff -> jpeg (if I am making outside edits in gimp or PS)
You pretty much covered all that already @buddingphotographer…Just wanted to add my 2 cents.