Do I need TTL...?

Let's quickly get the acronym out of the way. TTL stands for through the lens (metering) and it is an automatic flash mode that some flashes can be set to. A kind of 'set and forget' flash mode.

TTL really comes into it's own when the action is fast paced, like a wedding reception for example. The subject and lighting changes so fast that you don't have time to manually work out and adjust flash power. Taking our wedding reception example, the whole dancefloor and flashy lights thing makes TTL invaluable. 

You pay for the privelage of TTL though...  

You really don't need TTL if you're in a studio setting or have a consistent setup, for example product photography shooting or indoor/stable weather portraits. You'll just set your power to whatever creates your desired exposure relative to your overall exposure, again an example would be setting your flash power to 1/4 power or 1/2 power.

I personally started out with cheap speedlites without the TTL ability and I'm thankful I did. It made me force myself to learn manual flash, and it really isn't hard.  

You'll benefit the most from learning manual flash and having TTL as an extra tool. Having the ability to adjust power manually incase TTL fails will give you peace of mind in all situations. 

So, is TTL for you? That depends on what you shoot... But for the most part, a manual speedlite and a little knowledge will go a long way in creating beautiful photos.