Let me start by saying online training plans, plans found in a book, anything that is “pre-made” in a sense is inherently positive if it results in someone getting out the door and getting a run done. The issue with most training plans however, is that they are geared towards a specific race.
While you may be able to nail every workout, every split etc. for that training plan and do great for the specific race - the focus on the short-term is an important distinction to make. With a shorter term workout plan, sometimes comes the mindset that you must complete the workout as it is written, and that doing so will leave you fully prepared for the race.
The thought that nailing every workout (which rarely happens in real life) will equal X time in the race is a flawed one and can set you up for big mental failure before you truly even start. I wish every pre-made training plan came with a big asterisk that said “Expect that ALL of this can change...and that is okay.”
There are so many factors that play into what makes up your ability as a runner. For many of us it ranges from availability to train to stress levels. In order for the pre-made training plans to be truly successful, they need to be flexible if you have a surprise issue at the office and need to cut your run short. Here is a very specific example:
You have a really long day at work, you come home and haven’t eaten dinner (or lunch for that matter) and you have a 6 mile tempo run planned. It’s 9pm and you have a choice to make. While you could do the full tempo run, chances are you will be doing so exhausted both mentally and physically.
This will not have the same effect on your body as if you were fresh and feeling good. Alternatively, cutting your run in half may be enough to get some similar adaptations given your level of stress and lack of calorie intake. This will also allow you more time to sleep and recover mentally and physically for both running and life!
Stress is cumulative, and pre-made training plans ignore that. Please use them if you find them useful, by all means, anything that helps people run I support!
I would encourage you to approach it as a loose outline, rather than something etched in stone.