I should mention that I've run plenty of tempos in the past but not now. The problem is recovery, or lack of.
Personally I'm aiming for almost instant recovery from any training session I do. A sign I'm right on top of the loading levels.
We do need to overload to some extent but if I'm still feeling the residue from a training session 48 hours after completion then I deem the session inapropriate.
I need a fair amount of control during testing sessions. With a fast steady run I lose control, getting clumsy when tired and ship too much damage.
That's what I get from a tempo run so I avoid them. If I want to mash myself in one long hit, then I'll do it in a race.
I'm aware that they are a favourite with many runners. I discovered they were a good way of masking residuel aches and pains, probably on account of the levels of heat and endorphins kicking in.
Unfortunately, going out the next day became a problem.
Each to his own on this one.