Leica lens profiles have an intent which you should understand: They are an effort by Leica is to allow lenses that may or may not ever have been designed for a digital sensor to render as closely as possible to their original design intent. If you choose not to use them, the rendering they produce will just be whatever the lens's optical design does with whatever given camera sensor you're using them on; if you choose to use them, the rendering should match very closely from Leica camera to Leica camera, both film and digital.
For some lenses, they allow the lens to achieve its best performance on a given body and without them there are imaging issues that you have to accept and/or work around. For other lenses, the differences with or without is inconsequential.
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