If you use rates you do not need to set up Daily Prices for every day. If required you can use a Daily Price to adjust the prices for an individual date or date range.
If you are using Daily Prices The booking rules for your rates and Rates you daily prices will determine which daily price or rate will be used. You can define your price strategy in SETTINGS -> BOOKING RULES click on "Daily Price Strategy" to open and select if your daily prices can be undercut by rates ("Allow Lower Prices") or cannot be undercut by rates ("Do Not Allow Lower Prices").
Note: Rules in Rates have no effect on daily prices.