If you are happy with the clarity of the beer you are making you do not have to do secondary. A secondary
will result in a clearer beer. If you purge all your equipment with Carbon Dioxide you do not have to be
concerned about oxidation. Also, if you are meticulous about cleaning up your equipment and area immediately
and sanitize everything, you don't have to worry about infection. If you opt not to go secondary, just don't leave it
in there for months before getting it off the yeast. If you leave it too long, you can get some off flavors.
When I made my Kolsch, I cleared it in secondary with gelatin and a cold crash to get an extremely clear beer.
Since samples were going to a German Kolsch drinker I went to great pains to clarify it more. This beer style calls
for a really clear beer...not like a hazy IPA.