The vector shape paths can be used as a great source for Photoshop selections. In a variety of different ways. You can then use the result for fills, adjustments and more
Go to one of the vector tools, custom, rectangle etc and then go to the top left and set to path and then go to the operations and set to combine and also select a preset. Apply it, You can then go to the paths panel and right side menu and make a command and set anti aliasing etc. You can also create more complex artwork by adding multiple presets using the combine as well as subtract. At the end, go to the direct selection tool and select all the points and then go to the panel and the make command.
Apply the shape / path in quick mask mode. Can be entered via the bottom of the toolbox. Add a design but this time in pixel mode (top left) in black or grays or anything other than white. White removes, black adds. On exit from quick mask, you will then have to invert it via the select menu
Go to the channels panel, right side menu and create new channel (alpha) and use it. Apply artwork via the custom, rectangle etc and set to white and pixels option. On finishing with the designs, go to the select menu and load selection and alpha and you will see the marching ants from that design, basic or complex.
Layer menu and New layer and goto the Custom shapes tool. CSH presets / artwork to that layer (you can add one or multiple artworks). Select menu and load selection command. Select the channel 'layer 1 transparency' for the marching ants.