Test tube holders are used to distance a person from potentially dangerous tasks when using chemicals in test tubes. They not only extend a person's reach, they protect the user from harm while performing basic lab tasks.
Reference.com defines a test tube holder as a clamp made from metal, opened by squeezing the handle, that is used to grab test tubes with the far end. The handle insulates the user from harm if an exothermic or endothermic reaction takes place in a test tube, which could potentially burn or freeze a person's hand. Test tube holders add to a person's reach, allowing them to heat the contents of a test tube in the flame of a Bunsen burner without risk of burning themselves on the flame or the heated glass. They also provide distance when pouring liquids from one test tube to another, protecting the user from volatile reactions which might spew out heat, sparks or harmful chemical fumes. If the test tube breaks during the course of use, proper use of a test tube clamp prevents injury from the resulting glass shards. Test tube holder use is considered standard practice in any lab situation using potentially volatile chemicals or chemical reactions.