Bandwidth and hosting implications.

So, what does the average siteowner need to know about bandwidth?

Absolutely nothing!.........
If you have enough of it.

Bandwidth refers to the amount of data transfer per second.

Its standard unit is

kilo bits per second.
In a somewhat larger scale, it can be called

Mega bits per second ( in the order of one million bits/sec. or ten to the power of six )
Giga bits per second (in the order of one thosand million bits per second, or ten to the power of nine )

The slowest part or section of a route will limit previous and post transmission speeds to that mamimum.
In other words, you can typically have a few thousand miles of fibre optic cable, capable of high speed, and then be limited by a slower section of copper wire.
Likewise for a high tech network and a dial up modem. These variables are considered when working out the "throughput" value.

Wire less( whether infra-red or radio transmission) cannot compare to the bandwidth provided by fibre optic.
Similarly for copper conductors.
This is primarily due to their respective, physical properties.

Theoretically, nothing is faster than light though particle accelerators come near, but that is another matter, lol.
Sticking with bandwidth though - most people are currently stuck with copper somewhere along the line.

For a hosting plan, bandwidth has importance to the ambitious, as well as the successful. If a web page is downloaded often (successful), then bandwidth exceeding its number of kilobites multiplied by the number of downloads at a given time must be considered. This is without any other pages that may be on the site.

If a product or application (whether free, or not) has to be facilitated for download, then bandwidth must increase.

Where it is the case of globally popular downloads, mirror sites are used to lessen the burden as well as shortening the physical distance between server and recipient. When such a distance is shortened, then it should be cheaper for the recipient who may be on a dial up modem.
And in an ideal world, the likelihood of "slow spots", should theoretically, decrease.

In the case of flat rate I.S.P. accounts, energy is saved whether the time difference is noticed, or not, and unnecessary use of an unnecessary network is eliminated.

What you really need is an idea of how busy the site is, from a viewing perspective, and an idea of how much data is likely to be downloaded. Advice can always be sought from your host-to be.
But the idea would be to anticipate all data traffic, or get enough bandwidth, or ensure that it can be upgraded.
From a hosted site perspective, you will have done all you can to provide an uninterupted service, and any issues thereafter, are not your concern and outside your control.

Mirror sites are done by simple arrangement and the products or applications are stored on different servers at different geographical locations. Visitors can be directed to a site/location which they select to be closer. Any monies that may be involved is a matter of trust, to some degree, but payments can be made to the same payment processor and some traceability is maintained.

In conclusion, if you have enough disc space (which should be apparent enough ), enough bandwidth, and a reliable server with anywhere from 98% upwards of uptime, then bandwidth and its hosting implications should be covered.