Ok the first drama I watched with a time jump was My Girl, and I loved it there! I think they used it to show how their feelings were real and prevailed even though they didn't know they would ever be together again.
After that, I started noticing that most kdramas have this kind of thing, and sometimes it's good but other times, it really is just cliched.
The most stupid time jump I'ver seen was the one on You're Beautiful. I mean, is that even considered a time jump? It was just really lame and not put to good use, it didn't show anything, just the need to end a drama in the most predictable way possible.
Also, the Lie To Me time jump (or maybe the whole drama, I don't know) was really idiotic, for me. I thought it only looked like a cheap copypaste of Coffee Prince (I love the time jump there)!
Most of the times, I love time jumps, mostly because I think it would be awesome if that kind of thing happened in real life, but then there are always the exceptions I mentioned above