Explanation:

I'll be true with you.

As far as my knowledge goes (which is not far enough yet), as FRICTION is a type of dissipative force that always opposes the relative motion between any two objects (Note : this relative motion occurs between the surfaces in contact of the two objects) so it would decrease the kinetic energy (as it is opposing in nature) only if no external force is applied (equivalent to the value of frictional force) in the direction of motion (i.e. opposite to the direction of friction).

So I might SAY that frictional energy has its IMPACT on total mechanical energy of an 'object' which is that final mechanical energy would not be equal to initial mechanical energy as some energy might have lost in the form of heat energy produced due to the effect of frictional forces acting between the BODIES.

(Note: here I'm not talking about the complete system in which the body is present because if I do consider a system rather than just a body then my answer for your question will change…that'll be - 'it has no effect on total mechanical energy…it'll remain conserved' as energy can neither be created nor be destroyed it'll be there in the system maybe in different forms)

I would love to be corrected if my answer for this question is WRONG in some way. So please do leave a remark if this satisfies your query!

Thanks.