Charred ingredients introduce bitterness and smokiness, which can either complement or overwhelm other flavors in a dish, depending on the degree of char and the other ingredients present.
When food is charred, the Maillard reaction and caramelization processes are taken to an extreme. This creates hundreds of new compounds, many of which contribute to the complex flavors we associate with grilled or roasted foods. However, beyond a certain point, these compounds become dominated by bitter and acrid notes. The intensity of these flavors can easily overpower more delicate or subtle flavors in a dish, leading to an unbalanced taste profile. For example, a slightly charred onion can add a pleasant smoky sweetness to a soup, but an overly charred onion will make the entire soup taste bitter and burnt. The key is to control the level of char to achieve the desired flavor without sacrificing the overall balance of the dish. The type of food being charred also matters; some foods, like peppers, can handle a higher degree of charring than others, like garlic, before becoming unpalatable.
If you accidentally over-char an ingredient, try adding a touch of sweetness (like honey or sugar) or acidity (like lemon juice or vinegar) to help balance the bitterness. This can sometimes salvage the dish and prevent you from having to start over.