However in production it's better to make very gentle changes to a unstable house of cards even if it is utter shit held together by chewing gum and string.
To work in both you need to be able to switch between mindsets because they are really very different jobs. Someone working in both is not ideal. Even if you are very good at both there is a strong temptation to make radical changes, make incremental changes an place them in production and thus limit options in development or to develop something new that incorporates the flaws of something in production. An ideal is good communication between people in both roles.
"Switching hats" can result in too many compromises and being either too conservative or too radical for the project. If you are stuck in that situation external input from testers or somewhere is vital as a sanity check.