system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] Why does the transporter need a pad or platform on the ships? Why can't people just beam from anywhere on the ship?
gpt
They can, but it takes extra energy and is less efficient.   As you might have noticed it's usually only done in times where it's an emergency or much more practical to do spot-to-spot transports than transport-pad to/from location  (eg beam them directly to sick bay, etc).  They have even transported people directly from one location on the planet to another.  (far less often).

A typical transport has the subject being transferred at the transporter pad and into the transporter pattern buffer.   Then REMOTELY re-assembling that pattern elsewhere (planet surface, nearby vessel, etc) -- or in reverse, REMOTELY transferring the subject into the transporter buffer, and then re-assembling locally in the transporter room.   The "remote" portion of the process is the intensive part on the technology.

Now add the notion of receiving the subject remotely, into the transport buffer... then re-transmitting it remotely simultaneously to another remote location.

The transporter system is (in essence) doing twice the work.   It probably also has a greater margin of error should any portion of that signal be disrupted.

Star Trek Discovery spoilers:  >!In the 31st century we come to find out that transporter tech now fits in their com-badge.  There is no more transporter room, and they do indeed transport from point to point. !<