While cruising, for comfort reason, you are often ready to sail upwind slower but with less heal. In other words, you are ready not to sail at the best upwind VMG to preserve your crew. The upwind wind angle limit has been added for that reason. Say, you do not want to sail upwind closer than 55° of the wind direction, simply enter 55 for that parameter. As most polar curves are pretty flat close to the best VMG, you might be surprised by the small additional time your passage might take compared with the gain in comfort.
Here is an example of a passage from Les Sables d’Olonne to A Coruña on a Sun Fast 3200 where roughly half of the passage is against the wind.
No limit
45° limit
55° limit
65° limit