When new my bike had all Shimano components.
When it was time to replace the chain, the LBS installed an SRAM chain.
Was that a mistake on their part (if so, was it a bad mistake)?
I had a problem subsequently, and wonder whether the parts are quite compatible/interchangeable.
Edit -- I thought I remembered someone's saying on this forum that chain and cogs are specially shaped, to help the chain jump from one cog to the next when you change gears; and that this shaping is somewhat manufacturer-specific: so mixing them makes it harder to shift gears.