Dumb question, but do I need a knob lock if I have a deadbolt?

I'm moving in a couple weeks I've been looking at those keypad deadbolts (I'm a cyclist and the idea of not having to bring keys with me when I go out is very appealing) that can be opened either with a numeric code or with a regular key. However, I still have a regular doorknob lock too.

Is there any reason to bother with the doorknob lock if I've got a properly installed deadbolt? I've looked online but everyone else seems to be asking the opposite question (if they should get a deadbolt).

The house currently has 'Defiant' brand deadbolts and knobs, but I'd like to replace them since the previous owner, real estate agent, and who knows who else has copies of the keys. Ideally, I'd have just one key for the whole house, and I'd like to have a keypad lock on the back door at the very least, maybe both.

So I'm not sure if I should

1. Replace both deadbolts, unlock the knobs and put a piece of tape over them so nobody accidentally locks them

2. Replace the deadbolts and replace or rekey the knobs to use the same keys as the new keypad deadbolts, but avoid using them

3. Replace the deadbolts and replace the knobs with knobs that don't have a lock in them

I don't want to compromise security, but if I get a keypad deadbolt, it won't help me at all if the knob is locked, and I imagine the deadbolt is much more secure than the knob anyway.