I offer every 2-3 hours whether he asks (or when he was younger acted hungry) or not. Mostly before he was 6 months or so I would notice a supply dip if I let him go much longer. Nothing tragic but I assumed it was a sign I needed to offer more frequently. If he refused of course that was fine too.
The only problem I ever had was that my kid is weird about NIP. he'd really prefer to nurse lying down in the bed, although he nursed at parks and stuff all summer. Basically any distraction upsets him. Unfortunately I've had episodes where he won't nurse before we leave but starts crying for milk on the freeway stuck in traffic. That completely sucks.