Single digit chains?

I've been using the sudoku.coach app and is just finished with skyscraper, two-string kite and crane. The thing is haven't used them at all in the chapters. Are they just "shortcuts", making puzzles easier, or are they ever something you must use to move on?

I haven't really got a hang of weak and strong links either. But I do a lot of chaining without thinking about it (I've always done that, long before I started with the app and just did books no harder than 3), could it be that I'm chaining them in these patterns but don't realise it? I've really tried to find them!