If you plan to do lap swimming, then 32' length is pretty much the minimum to not be annoying in terms of the short distance between turnaround. The width is usually around 16' in that situation (i.e. 16' x 32' is fairly standard if you are going with a rectangular pool). 6' depth is also pretty standard unless you plan on doing diving. The con with a pool much larger than this is mostly maintenance cost since it will require proportionately more chemicals. As you can see from the link earlier in this thread, freeform pools are more interesting to look at, but are harder to cover.
There are always trade-offs. If you want to save on chemical maintenance (but have higher pool cover replacement costs) and don't want fencing or alarms preventing young kids from getting into the pool, then you can get an automatic mostly opaque safety cover. In that case, a standard rectangular pool with an undertrack cover works well for new construction, but doesn't look as interesting. You should also consider solar heating if you want to extend your swim season and possibly some automation including remote control of your pool equipment. At some point your budget will restrict what you can do and you'll need to prioritize.
