Oh yes using a longer lens to avoid being in a thorny rose bush looks like a good reason to me. 
You are also less likely to be casting your own shadow over the subject as well. If you change your mind about photographing insects you will be less likely to disturb them as well.
You are also less likely to be casting your own shadow over the subject as well. If you change your mind about photographing insects you will be less likely to disturb them as well.
