I use it fairly often, but with that said, I more often don't, and you might find my reasons for fast traveling a bit different than what you might think. Early in the game, I often find I need to go to far places to acquire this or that... Maybe I want to buy spells, and I don't want to go to whiterun yet and start the Main Quest, so I take a carriage to Windhelm, or solitude, or even Winterhold.
I have a mod that allows the carriage trip to be exactly that... Not fast travel, but sitting in the wagon and actually riding the entire distance.... or having the driver wake me when we get there, which is essentially fast travel. the reason that I might go with fast travel is simply that I don't want to see what's on the road between here and there, because I want to walk it later on and actually encounter whatever is there. I hate traveling early with a companion, because they insist on fighting everything that is encountered, especially that trip with Delphine.
Later, I walk every road at least once, but then sometimes I will fast travel if I have to retrace my steps over a road I've just gone down. Like traveling Riften to solitude for the thieves guild, then having to go back the same day or the next day. that gets dull.
At the same time, if you're always fast traveling, you aren't having as many encounters with random dragons and various creatures as those who walk the roads. Your game is going to be much more tame by comparison. Not many cave bears and giants in Whiterun, either...
To sum up, fast travel is fine occasionally, or to preserve an area for later investigation, but if you want a more interesting game, walk or even ride a horse or travel in a carriage that doesn't fast travel.