All my life through all the schools I have been to, they were teaching me how to properly design objects and services. You need to pay attention to every single detail and make sure that it satisfies all design principles and rules. This approach produces high quality results and it led me to win some prestigious design awards. So if it works, why changing it?! Well, the fact is that most of my professors were working for large companies or design consultancies. Large companies have a dedicated time for R&D and a big team, as a designer you can focus on designing all the details and making everything perfect. On the other hand in design consultancies, the only value of quality is how well something is designed so attention to details is a selling tool. They might spend less time on it than large companies since they have multiple projects running at the same time, but still they spend significant amount of time making sure that everything is perfect. They have to since their pitch is: "the design you currently have sucks, we can do it better". The problem is that this kind of thinking is also transferred into small companies although those companies need something completely different.
Everyone who has ever worked in a startup knows that the deadline is always yesterday. There is always something to do and designers often end up doing other things besides design such as marketing and sales. In those circumstances, how much time a designer have to make things perfect?! Still, I saw many designers in small startups adjusting kerning and moving things pixel up and down. When you catch yourself doing it, ask yourself how many people who are not designers actually see that? What is the purpose of your design? Most often the goal is not to make a perfect looking app, but to make a realistic enough solution that you can test. At least good startups should quickly make and test solutions if they follow lean startup ways. Problem is that very often even the startup founders and CEOs often overlook this fact. They have an idea what their "child" should look like and they want only that solution. In such case designer should remind the owner that design that you use for the first testing of the app is not the final one and that you will learn much more if you test now and not in two weeks when the "right" design is done. So, how should a designer approach his/ her tasks in a startup?!
First, every design is temporary and you should approach it like that. Most likely, the solution will fail the user test and it will be redesigned. There is no point to make things perfect in the first try.
Second, speed is everything. If you know about 80-20 rule, use it for design as well. You need 20% of your time to make a 80% good solution. In this circumstances, when most likely the solution you made will fail the first user encounter, it is good enough. There is no time for kerning adjustments and movings things one pixel at the time. You are the only one who will see those details anyway.
Third, you don't need to make three solutions and let your boss choose the one he likes the most. There is no time for that. Make a decision. You are the expert in the field. If you think it is good enough, it is.
Forth, the fastest way to design something is to make a mockup super fast and test it. Make a quick and dirty prototype and test it with colleagues from another floor in your building. It will give you enough insights to iterate. Trust me, by going out and testing you actually cut time needed for designing, although it doesn't seam like that. Imagine finishing the design and then testing it and seeing that people simply don't understand the UI you created. You spend hours making the alignments and finalizing the design only to see that it sucks. It is better to make paper or phone mockups and learn that right away.
All this points are intended for working for a early stage startup that is still creating their product. The rules most likely apply to startups in other stages, but some adjustments are needed depending on the case. Anyway, although working for a startup doesn't bring too much satisfaction in professional sense, since you are most likely not entirely happy with fast results you had to produce, working for a small company gives you the pleasure to see the product and business development from the beginning all the way to production. You get much better understanding of real world - what goes and what doesn't, and it makes your future design more realistic.