Quick answer: Watch for not knowing your crash rate, unexplained churn and bad reviews, crashes you can't reproduce, and relying on player reports. If you can't see your crashes, you need crash reporting.
If your game ships to players, it almost certainly needs crash reporting, since most crashes go unseen without it. Here are the signs your game needs crash reporting.
Not Knowing Your Crash Rate
The core sign is not knowing your crash rate, you can't say how stable your game is or how many players crash, because you don't capture crashes. If you can't answer 'what's my crash-free rate,' you need crash reporting to see the most basic measure of your game's stability.
Bugnet captures crashes from the field, giving you your crash rate. Not knowing your crash rate is the core sign you need crash reporting, it's the basic measure of stability, and you can't have it without capturing crashes from the field, so the inability to answer 'how stable is my game' is a direct sign you need crash reporting.
Unexplained Churn and Bad Reviews
A sign is churn and negative reviews you can't explain, players leaving or complaining about the game being buggy or crashing, while you can't see the crashes driving it. Unexplained technical churn and reviews point at hidden crashes, which you need crash reporting to see and fix.
Bugnet captures crashes from the field, revealing the hidden causes behind churn and reviews. Unexplained churn and bad reviews are a sign you need crash reporting, since the technical loss has a cause you can't see, capturing crashes reveals the hidden crashes driving the churn and reviews, turning the unexplained into fixable problems.
Relying on Player Reports
A definitive sign is relying on player reports to learn about crashes, since most players who crash never report, so reports show you a tiny fraction. If your crash awareness depends on players reporting (or you have no crash visibility at all), you need crash reporting to see the unreported majority.
Bugnet captures crashes automatically, not dependent on reports. Relying on player reports is a sign you need crash reporting, since reports miss most crashes (most players don't report), so you're seeing only the tip and missing the majority, automatic field capture sees all your crashes regardless of reports, which is what you need to know your real crash situation.
Watch for not knowing your crash rate, unexplained churn and bad reviews, crashes you can't reproduce, and relying on player reports. If you can't see your crashes, you need crash reporting.