It's really a matter of personal preference. If you are looking for a fast and flowing track the 6" turns will put a damper on that theme. However, they do add technical complexity to the layout. The Tomy 6" turn is really more akin to a hairpin turn with the 1:64-ish sized HO slot cars, so if you are looking to bring in a Monaco style hairpin, they will suffice and still make for a very drivable layout.
I am definitely biased towards fast and flowing layouts when it comes to my own track designs. A large part of this is due to the fact that in my younger days the one thing that was always at a premium was long straightaways, mostly due to space limitations but track cost as well. Nowadays if you give me a set of dimensions I will always try to come up with a way to maximize the full extent of the dimensions in a way that yields more than its fair share of speed. Nothing saddens me more (in a non serious way) than to see a huge table with a track on it that is chopped up into lots of little straightaways and oodles of noodles. I'm not saying it has to be all drag strips with big turns connecting them, but I want more than just the requisite one long straight along the drivers stations. I also love carousel curves, especially when done up with large radius pieces. My least favorite thing on a track is square corners. These tend to proliferate due to the abundance of 9" radius quarter turns. Nest a 6" quarter turn inside a 9" quarter turn and I'm already twisting the choke up to halfway even before I put my car on the track. The new Tomy 18" radius turn is the best thing to happen to set track in 30 years. If they do a 21" it will be the next best thing.
Tight corners are not the only personal preference feature. Some people like over-unders and some people hate them. Same goes for elevation changes and banking. Some specialty track pieces, like squeezes, wiggles, the 3" hairpin, crossovers, etc., fall into the fringe area of desirability. But if you like them, anything goes.
Design your track to fit your personal desires and incorporate the features you really enjoy. Unless you go too far out to the extreme fringe areas it's highly likely that others will enjoy what you have created too.
