[Elecraft] [K3] CW transmit filter bandwith

[Graham Smith]

I was reading W8JI's article http://www.w8ji.com/what_causes_clicks.htm but
see that the advice in it (use a narrower filter than an SSB filter for
transmitting CW) conflicts with the K3 manual, which says:
"Rotate VFO A to select a CW transmit filter (2.7 or 2.8 kHz). Note: Key
clicks may result if a narrower filter is selected for CW transmit."
Of course I will take the K3 manual's advice, but I am wondering why a
narrow filter can cause key clicks?

73 de Graham G3ZOD FISTS #8385
http://www.fists.co.uk