SDI is purely unidirectional. You can pass it through a distribution amplifier, split it one-to-many, plug and unplug cables, or whatever. It won't skip a beat.
This represents a major difference to HDMI. With HDMI, the display or sink device communicates its EDID to inform the source what its capabilities are such as resolutions, color formats, bit depth, and more. With SDI, the transmitter just sends the video stream and the receiver must be compatible or it won't work. Again due to no sink-to-source communication, SDI has no HDCP or other content protection. This means that most or all HDMI-to-SDI converters will not perform HDCP negotiation on the HDMI side. That implies that a source such as a Blu Ray player may not transmit video to an HDMI-SDI converter, or limit to 480P if it does work at all. There are ways around this, but it is a headache if you try to use HDMI/SDI conversion outside of (HDCP-free) pro video. Computers typically do not require HDCP, but if it is not present, then some types of content can become restricted, even things like web-based playback of Netflix or Youtube.
It might be the HDCP handshake that necessitated the custom solution your company created.