Using geometry rather than geography data types in SQL Server Spatial?

There's a good answer over at Stack Overflow, which goes a little something like this:

The geography type is a little bit more restrictive than geometry. It can't cross different hemispheres and the outer ring must be drawn counter-clockwise.

The rest can be found in Geography data type vs. Geometry data type in SQL Server.

A Geometry vs Geography article at the SQL from the Trenches blog goes into more detail:

If you’re looking for the biggest difference between the two datatypes, you’ll see it’s the functionality. A Geometry object is just a 2D, flat polygon. This means, it doesn’t matter if you take a country on top of the earth (for example Canada, which is “curved”), or a country close to the Equator (for example Brazil, which is “flat”).

A Geography object on the other hand, is a 3D (or even 4D) polygon, that has the same curve as the shape of the earth. That means that the difference between 2 point isn’t calculated in a straight line, but it’s need to consider the curvature of the earth.

Another crucial difference is the ability store your data in standard coordinate systems, such as NAD_1983_StatePlane_California Zone 5, and use all the capabilities of the spatial database, spatial functions, etc. and most importantly the spatial accuracy of a localized coordinate system - whereas sticking with geography as your data type, you can only store your data in WGS84.

So I'd say if you have the option, go with geometry, use EPSG: 102645/102245 (you'll have to check what is the standard 'state plane zone 5' for SoCal) and you'd be all set for any analysis you want to undertake. If you want to share, export your datasets to WGS84 if that is preferred for sharing.

Maybe check out the properties of Projected Coordinate Systems, to get a view into their utility?

There are 3 aspects or properties presented in Projected Coordinate Systems that establish their utility and rationale. Any projection of 3D space on a 2D surface will of course exhibit distortion versus reality. Depending on your application, using a specific Projected Coordinate System can ensure a more accurate representation of reality, and in some applications, fine grain accuracy matters.

Three properties of Projected Coordinate Systems. You can have perfection in some, but never perfection in all:

Equidistant - Distances (from a particular spot) shown on the map are true to reality.

Conformal - When zoomed in, the angles shown on the map are true to reality.

Equal Area - Areas recorded on the map are equal to the areas of objects in reality.