Failing to be punctual is the height of bad manners and will make you look unprofessional. Conversely, being punctual always scores bonus points. You will come across as someone who is efficient, organised and reliable.
By being late for a meeting, you are effectively forcing your colleagues or clients to waste their time; hanging around waiting for someone to show up is deeply frustrating.
Make sure you arrive for work punctually, or even better a few minutes early. This will ensure that you are ready to start the day on time. Workers who are consistently late are usually noticed for the wrong reasons.
Given the vagaries of transport systems, the tendencies of meetings to over-run, the unpredictable emergencies of modern life, you cannot expect to be invariably punctual.
If you see that you're going to be late, pre-empt the fall-out and call ahead.