Tell me when it matters.
A report on a schedule is a rhythm — useful, and easy to stop reading. A signal is an exception. It watches one thing, emails you the once when that thing happens, and then it is finished.
One thing, once.
It fires and it is done
A signal is not a subscription to a number. When the thing you were waiting for happens, you hear about it — and then it stops, rather than joining the pile of alerts you have learned to archive unread.
Set it from a goal you already have
"Tell me if I fall behind on this" is the common case, and it does not need a second definition of what "behind" means. A signal can watch a goal you have already set.
It goes where you already read
Email by default. On plans with chat delivery, Slack or WhatsApp — the place you would actually see it, not another inbox to check.
Why so few alerts, on purpose
Every monitoring product ends up training people to ignore it. The way that happens is always the same: alerting is free to add, so more gets added, and the ones that mattered arrive alongside the ones that never did.
Signals count against the same allowance as scheduled reports, because from your side they are the same promise — Glance will email you — and an uncapped second allowance is how a product ends up sending more than anyone reads.