Add section explaining filtering

Author: pwseg

src/unify/unify-event-filtering.md

@@ -7,15 +7,15 @@ Unify Event Filtering lets you control which events reach your Unify space.
 
 ## Overview
 
-With Unify Event Filtering, you can use block events that aren’t useful for identity resolution or downstream activation, keeping your space cleaner and more efficient.
+With Unify Event Filtering, you can use block events that aren’t useful for [identity resolution](/docs/unify/identity-resolution/) or downstream activation, keeping your space cleaner and more efficient.
 
 Event Filtering is useful when you’re sending a lot of different event types into Segment but only some of them are relevant to Unify. For example, you might want to:
 
 - Drop telemetry or system events that don’t describe user behavior
 - Filter out events from certain regions or user groups
 - Keep events in Connections, but exclude them from Unify
 
-Unify Event Filtering works differently from Destination Filters in a few important ways:
+Unify Event Filtering works differently from [Destination Filters](/docs/connections/destinations/destination-filters/) in a few important ways:
 
 |                  | Unify Event Filtering                    | Destination Filters                     |
 | ---------------- | ---------------------------------------- | --------------------------------------- |
@@ -24,3 +24,18 @@ Unify Event Filtering works differently from Destination Filters in a few import
 | Filter action    | Drops entire events                      | Can drop or modify events and fields    |
 | Setup            | Created through API, visible in Unify UI | Created in UI or API                    |
 | Timing           | Before identity resolution               | Before events get sent to a destination |
+
+This helps simplify your setup and reduce noise in profile data without needing repeaters, webhooks, or custom logic.
+
+## How filtering works 
+
+Unify Event Filtering evaluates every incoming event before it enters your Unify space. If the event matches any of your filters, it gets dropped.
+
+Keep the following in mind as you work with Unify Event Filtering:
+
+- Filters are configured at the space level. You don’t create filters per source. Instead, one set of filters applies to all sources connected to the space.
+- The filtering logic is based on [Filter Query Language](/docs/api/public-api/fql/). If you’ve used Destination Filters before, it works the same way. You can write expressions to match events based on type, name, traits, properties, or values.
+- Matching is inclusive: if an event matches any filter, Segment drops it.
+- Filtering happens **before** identity resolution; dropped events never reach the profile graph and won’t affect trait updates or [computed traits](/docs/unify/traits/computed-traits/).
+
+As a result, Unify Event Filtering helps you keep profile data clean from the start, without having to preprocess or transform events outside of Segment.