for the Points.
When iChat went Video in 2004 most people had a max of a Gb download and often much slower.
Uploads could be as low as 128kbps (there was an international Agreement that "Broadband" would start at 256kbps each way).
Although the Stated min is 128kbps this tends to be the Service you pay for.
However your Modem and computer have to maintain the connection to the ISP and that takes some of this bandwidth.
If you speed tested a 128kbps service you often only saw 105kbps of it "free" to use.
iChat would give you a complete Video failure message (it would not even attempt to connect) if it found Speeds lower that then the Dial up max (about 50kbps on a 56kbps device).
Since then processors and Internet Connection speeds have come on leaps and bounds.
The gap between what was Cable and DSL have been reduced.
I currently get "fibre to the Cabinet" (FTTC) at 40Mbps download and around 10Mb upload.
At a Max size of Video pic of 640 X 480 pixels at 30fps (or 0.3megapixels X 30 fps = 90 megapixels of data per second)
Obviously the Invite and Connection process can be as fast and if there are vast differences in speeds then one end can literally swamp the other end with data.
Screen Sharing is basically a Software camera showing you the Desktop (to start with) with a Audio Chat along side.
It have the same min as a Video chat.
8:00 pm Thursday; November 14, 2013
iMac 2.5Ghz 5i 2011 (Mavericks 10.9)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad