The two methods aren't necessarily mutually exclusive.
No reason why you can't automate tasks on manual trades. Adding stops, Tp'ing, partial TP'ing adding TP's to manualy opened trades, modifying stops, adding BE stops etc...
Trade sizes is a prime example. I got so tired of working it out I wrote code to do my trades, so all I'd do is put down a 1 unit trade to indicate where I wanted to trade then the code would come get the level, work out what I needed and do a properly sized trade for me at that level with the best spread it could find. No fat finger mistakes for moa and keeps the costs down.
The list is endless, those tasks are tedious so why not automate them, especially if you need to wait for something to move before you can modify open trades.
Or have drag and drop EA's when you want to perform manual functions, but would rather have the benefit if the computers speed and accuracy. Or the market is to fast to keep up or you want to try get a better spread etc. A good examle of that would be a partial TP, where my account is doing well, but I'm using to much margin so I want to drop say 30% of the account as a partial TP. I have an EA for that, just drag it on, wait till it's done and I only had to do one action. Takes 30 seconds instead of 5 minutes to do manually.
I think very few systems are fully auto. Decisions to switch them on or off are taken all the time.
So as things become a pain for you start defining them and then coding them and before you know it you have a semi auto method. Take it from there.