Totals Report for WooCommerce

No. It only reads your catalogue. It writes only its own data: settings and a few bookkeeping options (its version and next run times), the snapshots you take or schedule, its scheduled tasks (in WooCommerce's Action Scheduler), a 10-minute cache for the Dashboard widget, short-lived notices and locks, a per-user flag when you dismiss the upgrade notice, and, when the email report attaches the inventory list, a temporary file in your uploads folder that is deleted right after sending.

Units in stock multiplied by each product's cost from the WooCommerce Cost of Goods Sold field. Variations use their own cost, or the cost set on their parent product (or both added together, when the variation is set to add its cost to the parent's). Products with units in stock but without a cost are listed separately and are not counted in the value at cost. WooCommerce stores a cost of 0 on a simple or variable product as "no cost", so such products show up in that list.

Units in stock multiplied by the current price (the sale price while a sale is running) or by the regular price, depending on your setting. Prices are used as stored in WooCommerce, with or without tax according to your store settings. Every export states the currency and whether prices include tax.

A product that belongs to two categories is counted in both. Parent categories include their subcategories without counting a product twice.

All products except those in the trash (you can limit this to published products only). Grouped and external products are left out because they hold no stock of their own. A variable product counts as one product; its units and value come from its variations, including disabled ones. When variations share the stock of their parent product, that stock is counted once (shown as "Shared stock"), valued at the lowest price among those variations that have a price, and at the lowest cost among them; if any of them has no cost, that stock is listed as without cost. Disabled variations are left out of this choice unless all of them are disabled; if none of the variations taken into account has a price, that stock is valued at 0 at retail. In the inventory list these lines carry a valuation note.

In stock, low stock (at or below the low-stock threshold of the product, of its parent product, or of your store, in that order), on backorder, out of stock, and stock not managed (available, but the quantity is not tracked). Every product is in exactly one state, so the five always add up to the total. A variable product is low on stock when any of its available variations is. Negative stock (from backorders) counts as 0 units.

Snapshots record what your shop held at the time the snapshot runs (large shops are read in batches, so a sale made meanwhile can show up), and the inventory list gives your accountant every item with its quantity and cost. They help with your inventory count; your accountant keeps the official inventory records.

No. A snapshot is stored separately and its numbers never change. You can rename or delete it, and the "Keep snapshots" setting can delete old ones automatically.

It is scheduled for 31 December at 23:59 in your site's timezone and runs through WooCommerce's Action Scheduler, which needs WP-Cron. WP-Cron runs when someone visits the site, so on a quiet shop the snapshot can be taken a little later. For an exact year-end count, set up a real server cron for WP-Cron, or take a snapshot yourself before the first sale of the new year.

Yes. The report reads WooCommerce's product lookup table with a few database queries, and exports and snapshots run in batches. When it finds products missing from the lookup table, or recently changed products that disagree with it, it tells you how to regenerate the table.

No. It reports the single stock quantity WooCommerce keeps for each product or variation.

Only if you choose so in Settings › Dashboard and data. Otherwise your snapshots and settings stay in the database in case you need them later. Scheduled tasks are always removed.