It is important for a person to think before they speak , refusal to think well before speaking could make the person say things which are very inappropriate and which could cause harm to others in different ways...
Speaking wrongly can cause so many unpleasant implications and that is why one needs to avoid the act , thinking deeply before every speech can help you to avoid saying the wrong things alot of times..
Nevertheless, if you ensure that you really train yourself to be able to think before you speak, it will help you to speak more intelligently and make you say more right things than the wrong things..
A wise person would know that it is good to be a better listener if they want to be a better speaker , listening rightly will make you to be able to avoid saying the wrong things , a better listener will be able to have the time and the effort that will make it possible for them to speak rightly or say things which won't be consider stupid or useless..
Some people just say some things out without even thinking about what they are about to say and they makes them to often look stupid because they said things which does not make sense or things which will cause more harm than good..
So we should learn to think deeply before we talk...I hope this helps..