As a single foreigner, if you have had an ARC for the last seven consecutive years, with actual physical presence in the ROC for 270 days each year, then you meet the basic "physical presence test" to apply for permanent residency. The financial requirements, good conduct requirements, health check requirements, etc. are the same for all applicants.
If you are applying yearly for an ARC, that ARC is based on your "purpose of residency", which for most people in your situation would be your job. Hence, in the future if you leave that job, you immediately lose your residency rights. If you have National Health Insurance, then that would be lost as well.
With permanent residency, your "purpose of residency" becomes permanent residency. While that is a kind of circular argument, nevertheless it clearly separates your job and your residency rights into two separate categories. Hence if you leave your job, your residency rights are not affected.
You have asked whether obtaining permanent residence makes daily life and changing jobs easier. Before I answer that question, let me give you some basic background information.
I personally undertook the goal of pushing for the establishment of a category of "permanent residency for foreigners" in May 1996. After three years of lobbying in the Legislative Yuan, the law was passed in May 1999. However, this was only my perceived intermediate step in advancing an agenda of "foreigners rights". The final step is the establishment of free work rights for permanent residency holders, and other select categories of foreigners. I have been working on this proposed legal revision since June 2000, when we had a large Public Hearing in the Legislative Yuan to discuss my recommendations with different party legislators, Council of Labor Affairs officials, and local labor groups. My June 2000 proposals for changes to the Employment Services Act were adopted as part of the official CLA version which was submitted to the Executive Yuan, and then to the Legislative Yuan for action.
As I understand, the Legislative Yuan began reviewing these proposals in late March 2001. I am continuing to meet with legislators from all four parties, and the independents, to urge that these changes be ratified at an early date. Unfortunately, the pace of legislative change in Taiwan is slow, as you will have noted from reading the newspapers.
Hence, to answer your last question, when and if my proposals are ratified by the Legislative Yuan, permanent residency holders will have free work rights. They will be able to work in the company of their choice, or sell sausages in the street, or whatever. That is the final goal, however I am sorry to say that I have not quite reached it yet.
[Moderator's Note: The proposals for unrestricted work rights for permanent residents and "foreign spouses" were included as Article 51 of the revised Employment Services Act promulgated by President Chen on Jan. 21, 2002. Implementation details were largely complete by mid-March, and this new category of OPEN WORK PERMITS began to be issued on March 18, 2002. Thank you Richard.]