The most significant implication is that you, the intending passenger, do not attempt to alter or otherwise deface the ticket, as it is the sole evidence of the contract which you have formed with one or more Railway operators and will be used to indicate the details of that contract when it comes to the day / time of travel.
Think of your contract as a committment to provide you with a service, similar to a promissory note. Only by presenting the unaltered document can the Railway personnel see what exact service you paid for. Because this ability to walk away with the sole evidence of the contract, and to keep it, trusts the passenger to hold something with a real financial value, it places the railways at risk of abuse - not unlike the risk that the banks are exposed to in allowing people to hold bank notes (where forgery and alteration are made difficult by the complexity of the design). To regulate this risk, Offences were created to capture the attempt to change tickets, similar to the offences in which persons might attempt to alter bank notes or other negotiable instruments or evidence of future contracts.
These are interesting times in which a whole raft of evidential documents which are held by persons are being transferred from paper to electronic equivlents, and being transferred in quite different ways. We could contrast the very different arangements for electronic money, vehicle tax, television licenses, stocks and bonds, etc.
I still have to handle some documents which will only be accepted if they bear the embossed seal of the issuing authority or their representative. I guess the days of persons holding the sole paper evidence of an agreement are numbered. But until then, we must expect strict regulation of how they are to be treated and whose property rights apply to them.
