Small guns can be carried in horiz/ diagonal SH over the t shirt , under the outer shirt . accessed thru stratically unbuttoned button ( or western style snaps) . Not the fastest draw . but unlike ankle holsters , you can remain upright & moving .
Big guns can be carried in SH when you don't want them pulling down your pants .
I reference the period a cpl yrs ago recuperating from hand surgery when I was effectively one handed , and had to wear sweat pants . Vertical SH with 4 inch Service Six .
Full size guns in SH recuire more in the way of cover garments than a good pancake , but that's a trade off for you to decide .
I don't have problems with pancakes in the car , but SH are certainly good for driving