All network hardware, no matter how reliable, must be considered as a device that could  malfunction.  Network architects will assess the mission critical nature of any given link, what redundant or alternate data paths exist, and how service might be impacted if a service window were required to replace a device in that link.
In some cases an in-line device that has multiple links passing through it and may be an appropriate choice. But a more conservative design might dictate that no in-line device should ever tap more than one link – thereby eliminating the possibility that two links might ever be impacted if such a device had to be replaced. The most conservative or lowest risk designs may even require that the tapping be done by a  non-powered Physical Layer device such as a simple fiber tap and the task of aggregating the duplex data streams and making multiple copies for the tools be handled by a  separate device.
There is no right or wrong answer for such question – it will be determined by the individual circumstances and priorities of the organization – but such issues should be considered.