Not only will it make it less absorbent it will almost make it waterproof.
I unfortunately, like all good lessons learned from experience, made the mistake of spilling a well known brand fabric softener into the washing machine onto a load of new towels shortly after my DW and I were married.

I didn't realize it made clothes impervious to water when applied in copious amounts mostly because I had never spilled it into the washing machine before in that way.
When those towels came out of the dryer after several more washings, they were almost slippery enough to use as a waterslide.

I still hear about that one occasionally even after 5 years have passed.