I would like to say Coper is 75% right. Sometimes you should try to "widen" your slide. If you do a normal drift you can't force it as fast to a certain angle, or to not be forced to drive straight, or use a useless drift, to prove my point I will take Richard Taro's MCTP2 video.
First straight, boost laps. Instead of doing like Taro, if you widen the first left drift a bit just, then do a drift around the corners, you will gain time.
first refiller, boost laps. Richard taro drives straight for like 1 second here, loosing usefull 0"0x time, if you make a wide drift here, you won't lose "that" much angle, and hit the refiller, making your time faster.
I want to point out also there's different kind "widen", and that you have to use "widen" tech depending on track and place. But this is ofcourse only my opinion, I'm just trying to be helpful at times :)
Also tracks I would recomend:
MCTP1-2, MCMC and maybe BBBB :)
Edit: I know Coper doesn't say never to use it, but it almost sounded like it's bad if it's wide.