The Meaning of Life, the Universe, and Everything.
Only if you use too many of them. But as long as you use a condition to limit the execution of the actual command, you should be fine. This is because the condition will save power by checking if the command should actually run first before running it. Running a raw command every tick would lag more.
Rollback Post to RevisionRollBack
Remember those versions that minecraft pranked us with? Specifically:
Those are still downloadable! Watch this video for 2.0:
To download the other ones you need to make a folder in the versions folder for minecraft and put the client and JSON file for the versions in there. They all need to be named the same aside from file extensions. Once you do that, you will be able to choose that version when making a new profile with the minecraft launcher.