In which case Selenium IDE and RC can be chosen?

In which case Selenium IDE and RC tools can be chosen.
Can anyone have any suggestions for it?

This forum is more for the UI Vision Selenium IDE. But in general, you can use Selenium IDE tools for all kinds of web automation. The only thing I would not use it for is high speed web crawling, for that a non-browser solution is better as it is faster.

Selenium IDE should be chosen to know about Selenium and the concepts related to automated testing which include locators like name, id, XPath, CSS selector, and others. The users can also learn about Selenese commands like open type, verify, assert, click and wait, explore test cases in the various formats and execute JavaScript code with the help of runScript.

Selenium RC should be chosen if the testers want to test web applications with complex AJAX-based scenarios, to test an application against a new browser that supports JavaScript, to deploy tests over multiple platforms with the help of Selenium Grid, to run a test against different browsers on different operating systems.