Late labs lose points. Now the people who have cheated go in the lab without really understanding what is going on. These unprepared people either make life difficult for their lab partner or, in cases where both partners are unprepared, make life difficult for the whole class by working slowly, taking a long time at instruments and reagent stations, and monopolizing the Tas. They have to ask around for the answers to post-lab questions because they still have only a glimmer of understanding by the end of the day. They get little from the experiment.
Prepared people lose too.
Do your prelabs before heading for the lab. You'll perform better. Don't share your answers with others. They're using you. This is your education.