Why clock the lunch instead of entering minutes?
Estimating "about 30 minutes" hides drift: a lunch that runs 12:02–12:41 is 39 minutes, not 30, and over a week those extra minutes add up to real money. Punching all four times gives you the exact figure — the way a physical time clock records it. If you'd rather just enter a break length, the standard time card calculator uses a minutes column instead.
Are lunch breaks paid?
Under federal rules, a bona fide meal period — typically 30 minutes or more, fully relieved of duty — is unpaid, which is why it's deducted here. If you work through lunch at your desk, that time is generally compensable and you shouldn't clock it out. Short rest breaks of 5–20 minutes are a different category: they're normally paid, so don't punch out for them at all.
Some states go further — several require that a meal break actually be offered after a certain number of hours. If your totals here regularly show missed lunches, that's worth checking against your state's rules.