When to NOT to use Lightroom?

I think you might find it worth exploring plugins rather than PSE. I have been using Lightroom for a year, and I use PSE very occasionally. I have just started to look at other options, really for situations where I like the composition but the lighting is uninteresting. That's a challenge for me because I take a daily picture for BlipFoto and the weather is often unhelpful.

• I have used Topaz Adjust for images that lack interesting contrast. I'm still learning when it helps and when it doesn't.
  
• Viveza works really well for local adjustments. Give it a try if you find the Lightroom adjustment brush hard work or inadequate. I was all set to buy Viveza at the end of the trial period (and I still might buy it) until I found something else ...
  
• onOne's Perfect Photo Suite (Lightroom Edition) has a good range of tools for not much more than the cost of PSE. There are some tutorials under the Inspiration link on their website that I found interesting. Obviously they are intended to sell the product, but the  presenter discusses more general photography ideas too and usually combines use of the onOne plugins with adjustments in Lightroom.

Although I have been trying different options, my ideal would be to stick to a small number of tools that I use regularly enough to understand well. So I'm interested in other answers to your question.