What it genuinely protects
The concrete benefit is that your personal mobile number never enters a third party's database. That matters because phone numbers are durable identifiers: once a marketplace, dating app or forum has yours, it can be sold, leaked in a breach, matched against other datasets, or used for SMS spam for years.
Verifying with a number that is not yours breaks that chain for the sign-up in question. It also means a data breach at that service leaks a recycled number rather than your personal one.
What it does not hide
A virtual number is not anonymity. The platform you sign up to still sees your IP address, your device and browser fingerprint, your payment method if you pay them, and your behaviour on the account. Any of those can identify you regardless of which number you verified with.
It also does not hide anything from us or from the payment processor: a wallet has a payment history, and we keep the records any operator must keep. If you need genuine anonymity from a platform, a phone number is the least of the problems to solve.
The real risk: reuse
The single most important safety rule is not to attach anything you care about to a number you will not keep. After an activation ends the number returns to the pool, and a later holder can trigger a password reset on any account still pointing at it.
Use a temporary number for one-time sign-up codes. Do not use one as the recovery number on an account you intend to keep, and do not use one for banking, payments, or anything holding money or identity documents.
Codes are secrets, briefly
Treat a one-time code like a password with a short life. Never forward one to anyone, however official they sound — no legitimate support team ever needs a code you received. Most account-takeover attempts in this space are simply someone talking a user into reading their code aloud.
This is also why public "free SMS" pages are unsafe for anything private: they publish exactly that secret, to everyone, instantly.
Where the line is
Each service defines which countries and number types it accepts. Check its rules and choose a country consistent with the account details and eligibility requirements.
Illegitimate use is fraud, impersonation, evading a ban or law enforcement, mass automated account creation, or anything abusive toward another person. Our acceptable-use policy prohibits all of it, and accounts doing it are closed. A privacy tool is worth defending precisely because it is not a fraud tool.