Learn basic coding for what purpose?
Mark17, this is another topic one can write treaty on. If you work with computers at all, learning how to code can speed up whatever you are doing. Even simple watching Youtube can be improved by cutting off any adds (not to mention about blocking trackers and other annoyances). But let's focus briefly on trading only.
Back to BT - if you do backtesting JL style (for what I see it is very popular method) by coding your own auto-BT allows you to save huge amount of time over long run. What will require days or weeks to accomplish with ONE/OV can be dome in secs/mins when you automate the process. Then you keep a fresh mind to analyze output data while with ONE you are usually tired after long BT session. Next. With your own code you can extract exact data you are looking for while with O/O (ONE/OV) you are limited to what they offer. For example, if you wish to study behavior of third order greeks - no problem, if you want to track sqrt(vega*theta^2)/(3delta/8) ratio (make up example) - you can do it with ease and quicly compare how it changes across various trades. Heck, you can run autoBT on multiple trades or multiple trading rules at once and spent rest of the time analyzing data.
Or, to take simpler example, you can create a graph to see all delta changes through the time you were in trade.
There are automated BTs out there that you can buy/rent but they are not written with you in mind. If you want to use any soft written by somebody else you will cave to his way of thinking or you have to put extra effort to overcome this.
Trading - you can write tools to aid your trading. If you know what you are looking for, like this ratio I mentioned above or just simply to find best trade for parameters you use, you can write yourself such a tool - very doable if you know coding and quite helpful.
You can write code to analyze your past trades the way you want. You don't have to adjust your expectations to what O/O offer.
You can analyze markets in a way not available to O/O, to find edges for your trading - your imagination and needs are the limits and guide.
If you are trading multiple accounts you can manage those accounts from one place the way you want (Tom's example).
And so on, and so on. I can't think of all applications.
If you know coding you can tap to works of others willing to share solutions for free via Git and other sources and modify other's code to your needs.
All I said above refers to writing code for yourself/friends, if you want to write something to sell, like better ONE - then this is bit different story.
There are downsides of course. You have to spent time to learn some coding language. If you enjoy this type of activity - no problem, if you don't just code what is most important to you and be done. (Actually there can be a problem if you enjoy coding - you can end up writing lines of cool code that nobody needs, including you).
Other important issue is data for your code. You have couple options, some free, some paid - depends what you need. If you trade many underlyings ONE can be a good choice as plenty of tickers are included in subscription, but then, again - depends on what kind of data you need.
You got the idea.
I just want to repeat what I said before: you do not have to code to become a good trader.