If you're adding USB drives or other USB devices, please note that the maximum current the Raspberry Pi 4** USB ports (either combined or a single USB port) can pass through is 1.2A.
To clarify, you cannot draw 1.2A from all four ports at the same time. You can draw this from one port only, or 1.2A across all 4 ports combined.
HDDs (traditional spinning disk drives) tend to draw a lot of current and are not advised to be used with the Raspberry Pi via a USB adapter. Instead, use an SSD which draw much less power than HDDs.
** and Raspberry Pi 400