Mash temps for a single infusion mash should generally be between 148 (light body) and 156 (full body). Much below 148 and you start to get thin, dry and over attenuated. Much over 156 and you start to shut down conversion and get under attenuation. The 168 is for mash out to stop conversion and "lock in" the mash profile before an extended fly sparge. If you batch sparge, you don't really need it.
Once you get into multi-step mashes, you can play around with different temperature ranges to accomplish different profiles. Part of the reason many Belgians have FGs close to 1.000 is that they spend a lot of mash time in the 130s and 140s (that and a lot of candi sugar). I just did an Oktoberfest with three different temperature steps. I'm not sure my pallette is sophisticated enough to tell the difference between that and a single infusion or decoction mash but I take the word of people witb a lot more knowledge than I that it does make a difference. More importantly, I like the results. It's also a fun challenge to manage the whole process.