Browning mince (ground meat) before putting it in a slow cooker is not strictly necessary, but it is recommended for several reasons:
Flavor development: Browning the mince in a pan before adding it to the slow cooker caramelizes the meat's surface, creating a richer, deeper flavor in the final dish. The Maillard reaction, which occurs during browning, enhances the overall taste.
Texture improvement: Browning the mince can help improve the texture of the final dish. It reduces the likelihood of the mince clumping together and gives it a more appealing appearance.
Fat rendering: Ground meat, especially beef, can release a significant amount of fat while cooking. Browning it first allows you to drain off excess fat, resulting in a leaner and healthier dish.
Safe cooking: While a slow cooker can ultimately cook raw meat thoroughly, pre-browning the mince ensures that any potential bacteria on the meat's surface are killed off before the slow cooking process begins.
If you're short on time or prefer a more hands-off approach, you can certainly add raw mince directly to the slow cooker. However, for the best flavor and texture, taking the extra step to brown the mince beforehand is recommended.