A weak or reused password is still the single most common way personal accounts get compromised — not through some sophisticated attack, but simply because a password was easy to guess, or the same one was used across multiple sites so a breach at one company exposed accounts everywhere else.
Generating a genuinely random password and checking an existing one's strength are two different, complementary tasks. A generator creates something strong from scratch. A strength checker evaluates a password you already have (or are thinking of using) and flags specific weaknesses — not just "weak" or "strong" as a vague label, but concrete issues like length, predictable patterns, or whether it resembles commonly-breached passwords.
One genuinely important distinction: password strength and password memorability are often in tension. A long, random string is strong but hard to remember without a password manager. If you're not using a password manager yet, a passphrase (several unrelated words strung together) is a reasonable middle ground — still hard to guess, easier to actually remember than random characters.