What are the reasons for and against using normalized floating point?
Binary IEEE format include both normal and denormal ('subnormal') numbers. The purpose of subnormals is to avoid a gap between the smallest normal numbers and zero larger than the smallest difference between consecutive normal numbers.

This gap make generate instability in some calculations dealing with small numbers,...
Denormal have a performance and/or complexity cost in software and hardware. Sometimes denormals are not handled or a fast mode is provided where all denormals are considered as zero.

(Here is an historical perspective from William Kahan, one of the original creators of the P754 format: https://people.eecs.berkeley.edu/~wkahan/ieee754status/754story.html)