Actually it does, running lean or even a too hot plug can cause an engine to overheat and lose compression. It usually returns when it cools down. A hot run also means there will be less oil film in the cylinder, this will mean less compression till new oil can saturate the pores. Of course a lean run, especially with high nitro, could mean you cooked the engine and it is now worn out, or nearly so. But a TT is usuall tough enough to take a few lean runs.