Standard vs full port ball valve
Full port valve provide a flow diameter that is the same as the inlet/outlet ports.  So, for example a 3/4&quot; full port will be 3/4&quot; throughout.
A &quot;standard&quot; does NOT provide that and a 3/4&quot; standard has a flow diameter restriction of something less than 3/4&quot;.  Likely closer to 1/2&quot;.
Why use one over the other?  Full port costs more and takes up more space and offers little benefit for many applications.  So unless you have a specific need, chances are that the standard valve will be just fine.
If you have concerns about the flow or it's a relatively high-flow line then use a full port.
Generally the same principles apply to any fluid, water or gas, but gas is a compressible flow and is affected somewhat less.  Gas, at least as used in homes, rarely flows at a rate comparable to water.  But in some cases it may be needed to use full port.
Knowing when to use one vs. the other is not always obvious.  This is why engineers go to college for 4 years or plumbers apprentice for several years.