A level test and a certification exam answer two different questions. The first tells you where you are. The second proves it to somebody else. Mixing them up costs either money or time, depending on which one you get wrong.
The difference in one line
A level test is for you: free, fifteen minutes, worth nothing outside your own head, and it tells you where to start again. A certification is for an office, a university or an employer: it costs between one and two hundred euros, it is taken at an exam centre on a fixed date, and it produces a document.
When you genuinely need the certificate
Italian citizenship. Since December 2018 a certified B1 is required for citizenship by residence or by marriage. There is no way around it: no online test, however well built, counts. I have written about which certificates are valid and how they differ in this comparison of CILS, CELI and PLIDA.
Enrolling at an Italian university. Usually B2, sometimes C1 for certain faculties.
Public competitions and some employers. They ask for the document, not the ability.
Outside those three cases a certification is an expense that buys you nothing you did not already have.
The question that settles it: will somebody ask you to show a piece of paper? If the answer is no, you do not need an exam. You need to know where you stand, and that is free.
The mistake I see most often
Booking the exam before measuring the level. A CILS session costs money, runs only a few times a year and cannot be postponed. People who sign up for B1 hoping to scrape through, and arrive with A2 vocabulary, fail the reading paper and lose both the fee and six months.
The right order is the reverse: measure first, then pick the date. An honest test that separates the four skills tells you whether B1 is three weeks away or six months away, and the difference completely changes which session to book.
The other mistake, cheaper but slower
Putting the test off because «I already know I am a beginner». Almost nobody guesses their own level, and people who underrate themselves lose months redoing what they already know. How you perceive your level depends more on how you learned than on how much you know.
What a well-built test gives you
Not a label, a profile. Knowing you are B1 is worth little. Knowing you are a B1 with A2 vocabulary is worth a lot, because it tells you exactly what to work on for the next three months, and it stops you booking an exam you would not pass.
And if it turns out you do need the certificate, you reach the exam date knowing you are ready instead of hoping.
