We constantly should seek forgiveness (sincerely and genuinely from the heart) because doing so:
1- Shows we feel about the sin and that we really want to stop the sin. It shows we care.
2- It reminds us to avoid the sin as best as we can. When we forget the sin and feel normal committing it, we are less likely to change and it shows we don’t care about Allah.
Now it doesn’t mean we should improperly take advantage of Allah’s mercy, but it means we should never lose hope from his mercy.