It boils down to what you consider acceptable if your laptop is stolen, your laptop's drive dies, you accidentally delete a file, or a file gets corrupted. If you're OK with day-old data, then once a day is fine. For most people, there is no regular rhythm to important data... there'll be days of just email and web surfing, when backups are relatively unimportant. Then there'll be the day when you finish your epic manuscript when you'll want the hourly backups running.
If very little changes from backup to backup, Time Machine is very efficient about how much space is gobbled up, so don't worry there. People never regret backing up too much, only too little.