What is the importance of maintaining an isolated system in calorimetry experiments?

I know the basic parts - calorimetry is the experimental process of measuring changes in a chemical system & an isolated system is one where neither matter nor energy can enter or leave. Why is an isolated system so important though? I know you need very precise measurements of masses & temp. changes, but I need help to expand a bit more on this. Maybe with a specific example? Thanks!

1 answer

The isolated system allows no heat lost nor gained from outside, which would totally invalidate the data.