you'll get a lot of differeing opinions on this but in my opinion a strike indicator doesn't do anything the end of your fly line won't ( if you are attentive)
I think it is a rare occasion where a strike indicator will scare a fish.
Now here is where a lot of people will dissagree with me. I think indicators are a huge crutch and people rely on them far too much and as a result the development of their skills suffers. The reason they are so popular is that they are a no brainer to use and are effective even in the hands of total novices. Why? because they require no skill. Skill can be applied to them to make them more effective but skill is not necessary.
In my opinion indicators are for 1. beginners and 2 for people who only care about catching as many fish as possible. 3 have limited uses in specific situations for skilled anglers.