Add a section for when to use a collector (open-telemetry#1286)

Author: svrnm

Diff for: content/en/docs/collector/_index.md

@@ -10,19 +10,35 @@ aliases: [/docs/collector/about]
 
 ![OpenTelemetry Collector diagram with Jaeger, OTLP and Prometheus integration](https://raw.github.com/open-telemetry/opentelemetry.io/main/iconography/Otel_Collector.svg)
 
+## Introduction
+
 The OpenTelemetry Collector offers a vendor-agnostic implementation of how to
 receive, process and export telemetry data. It removes the need to run,
 operate, and maintain multiple agents/collectors. This works with improved scalability and supports
 open-source observability data formats (e.g. Jaeger, Prometheus, Fluent Bit,
 etc.) sending to one or more open-source or commercial back-ends. The local Collector agent
 is the default location to which instrumentation libraries export their telemetry data.
 
-Objectives:
+## Objectives
 
 - *Usability*: Reasonable default configuration, supports popular protocols, runs and collects out of the box.
 - *Performance*: Highly stable and performant under varying loads and configurations.
 - *Observability*: An exemplar of an observable service.
 - *Extensibility*: Customizable without touching the core code.
 - *Unification*: Single codebase, deployable as an agent or collector with support for traces, metrics, and logs (future).
 
+## When to use a collector
+
+For most language specific instrumentation libraries you have exporters for popular backends and OTLP. You might wonder, 
+
+> under what circumstances does one use a collector to send data, as opposed to having each service send directly to the backend?
+
+For trying out and getting started with OpenTelemetry, sending your data directly to a backend is a great way to get value quickly.
+Also, in a development or small-scale environment you can get decent results without a collector.
+
+However, in general we recommend using a collector alongside your service, since it allows your service to offload data quickly and the collector
+can take care of additional handling like retries, batching, encryption or even sensitive data filtering.
+
+It is also easier to [setup a collector](./getting-started) then you might think: the default OTLP exporters in each language assume a local collector endpoint, so you'd start up a collector and you'd just start getting telemetry.
+
 {{% latest_release "collector-releases" /%}}