Cutting the stems/spikes won't hurt the plant but the birds will eat the seeds of the spent flowers when they dry. I leave mine for the birds.

Deadheading is removing spent flowers from the stems, generally one seedhead at a time, but leaving the stems on the plants.

I got rid of all my liatris a few years ago because I really didn't like the looks of them. Now I'm growing more, both purple and white, because I learned the bees & butterflies love them + the birds eat the seeds.

I cut just below the spent bloom as the leaves are feeding the bulb for next years flower.I usually deadhead most of them so I don't get so many seedlings. If you want seedlings, let them go to seed.

I hope I get seedlings here! I love these plants.