Admit it, we all have a tendency to use large splitters when we could use small ones. Even though the large ones cost more, we put them in because we want to future-proof our systems. Since DIRECTV rolled out their SWiM system that allows the line to be split multiple ways, this has become even more common.
There's a good reason not to split the line more than necessary: line loss. Even a properly terminated splitter loses signal. In fact, the loss from a single 1x8 splitter can be up to 10 times greater than a 1x2 splitter. This means that you'll have problems on longer lines especially in areas where rain fade is common.
If you're an installer, you generally don't have a choice. In fact it's a good idea to leave the customer with one unused port, just so they can do a little bit of the work themselves if they want. However, some installers have been known to put a 1x4 splitter after a 1x8 splitter just because it's what they had in the truck. In this case it cost the customer another truck roll and a lost day of pay when the only problem was that the splitters were too much for the job.
If you're a DIY'er think about the absolute minimum you'll need to run the system you have. Put splitters where you can reach them later so that you can easily upgrade from a 1x2 to a 1x4 if you need. Home installations hardly ever need a 1x8 as they won't have 8 receivers very often. More likely they will have DVRs which only need one line to run 2 tuners. In homes, a 1x4 will usually do just fine. If you plan on splitting the line after a long run, use a 1x2 close to the dish and another 1x2 (or 1x4) where you need it.