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  • Hirofumi Takahashi thinks this is interesting:

Changing the bandwidth or delay of an interface should be done only for good reasons and only with a full understanding of the results of those changes. In most cases, it is best to leave the default values unchanged. A notable exception is serial interfaces. As noted earlier in this section, serial interfaces on Cisco routers have a default bandwidth of 1544 no matter what the bandwidth is of the connected link. The bandwidth command should be used to set the interface to the actual bandwidth of the serial link.

From

Cover of Routing TCP/IP, Volume 1, 2/e

Note

Note on bandwidth and Delay except serial interfaces