Advice on running flask app ONLY locally forever
Your idea is possible and while there are many ways to do this kind of thing, what you are suggesting is not necessarily to be avoided. 
All apps that run on a computer over a long period of time start a process and keep it going until closed. That is essentially what you are doing. 
Having done this myself (and still currently doing it) at my business, I can say that it works great. 
The only caveat is that to ensure that it will always be available, you need to have the process monitored by some tool to make sure that it gets restarted if it ever closes due to a variety of reasons. 
In linux, supervisor is a great tool for doing that. In windows you could register it as a service. But you could also just create an easy way to restart and make it easy for the user to do so if it is down when they need it.
I want to create web form that stays on forever on a single computer. Users can come to the computer fill out the form and submit it. After submitting, it will record the responses in an excel file and send emails. The next user can then come and fill out a new form automatically. I was planning on using Flask for this task since it is simple to create, but since I am not doing this on some production server, I will just have it running locally in development on the single computer.
I have never seen anyone do something like this with Flask so I was wondering if my idea is possible or if I should avoid it. I am also new to web development so I was wondering what problems there could be with keeping a flask application stay on 24/7 on a local development computer.
Thanks