Pretty horrible. Generally employers don't want you writing code for the following reasons:

They are paranoid you will steal from them the ideas you code on and compete.

They want to own your ass.

In either case, I don't like paranoid management, and I don't like people "owning my ass".

Now on the flip side I don't see why someone you TRUST can't own the company. You might program for it unofficially while working at your current company.