You must have seen such expressions during the festivals: 欢天喜地过大年/闹元宵。Why not use only 欢喜？What difference is there between 欢喜 and 欢天喜地？
天地 literally means heaven and earth, and is used very often with another two-word phrases such 欢喜, 长久, 昏暗, 惊动, 感谢, etc. to form four-word phrases, also called set phrases, to achieve the effect of emphasis, e.g. 欢喜 with joy 欢天喜地 with extreme joy；长久 for a long time 天长地久 everlasting and unchanging.
