For a long time Joomla has included a very powerful component to handle url redirects. This is especially useful after a site upgrade or redesign. Don't know how to use it? Check this great article explaining all the features by Ruth Cheesley in the Joomla Community magazine.
However it had a problem which probably meant that you looked at it, set it up and then quickly abandoned it for something else.
Joomla we had a problem
By default it collected ALL the urls that didn't exist on your site whenever someone tried them. That's not just real urls that may have existed at some time but also all those really odd and bizarre urls created by crackers who were looking for vulnerabilities
As a result the database table would grow very rapidly and with no method to purge the database it made the component pretty useless and very slow. On some web hosts with limited database space it could even bring your site down.
With Joomla 3.4 that all changed
With the recent release of Joomla 3.4 a new option was added to the redirect plugin by Viktor Vogel to disable the collection of all those useless urls.
Now you can use the component correctly exactly as Ruth described and when you have it set up with all the URLs you need to redirect you can disable the collect urls option. Now you get all the SEO benefits of a powerful URL redirection manager without all the issues I described and that you probably found for yourself.
I bet you didn't know about this Hidden Secret