Why should you reglaze rather than replace?

Well he first reason is to save both time and money! You can save 80-85% over the cost of replacing an item. For example, a bathtub can easily cost upward of $1,500.00 to replace by the time you tear out the old tub, dispose of it, buy a new tub and have it installed, have a plumber refit the drain and faucet, then have painters and tile setter fix any damage to walls and tile surrounding the tub. 

It is also very common in older buildings that to remove an old tub the doorway has to be widened or the the tub has to be cut in two.  These things add a lot of time and money to the project. 

If you are doing a full remodel that may be a time to think about replacing old fixtures.  But even then, some old fixtures should be kept and refinished because of their desirability as authentic items original to the home.

An extremely rusted, pressed steel bathtub should generally be replaced once the rust has set in. 

A second reason to repair and refinish instead of replacing, is that it is the right thing to do for the environment.  Recycling old fixtures helps the earth by saving earths resources and reducing the burden on land fills