The difference is not effort, it is reach. A regular clean maintains what is already in decent shape: kitchen surfaces, bathrooms, floors vacuumed and mopped, dusting at hand height, beds made, trash out. It is designed to be repeatable in a few hours, which is exactly why it works as a weekly or biweekly habit.
A deep clean goes after everything that regular visits never touch. Baseboards and door frames wiped by hand. Ceiling fans, vent covers, and blinds. Grout and shower buildup scrubbed rather than rinsed. The grease film on the wall behind the stove. Cabinet tops nobody has looked at since the house was built.
Here is the honest test: run a finger along the top edge of a door frame and along the baseboard behind a piece of furniture. If both come back clean, your house needs regular maintenance. If either one comes back grey, no amount of weekly surface cleaning will fix it, because that buildup is below the level a regular clean is designed to reach.
The usual pattern that works is a deep clean first, then a regular schedule on top of it. Starting with a regular clean on a house that has not been deep cleaned in a year means paying every week to maintain a baseline you never actually reached. Start at the bottom, then keeping it there is genuinely easy.
One more thing worth knowing: a deep clean takes noticeably longer than a regular visit, sometimes two or three times as long. Any cleaner who quotes both at the same price is planning to do one of them badly.