Unless of course you are that type of person who doesnt like wasting and are ok with swapping some of your maxed out tanks for low level ones to make them stronger while maintaining your main teams core.
For example since 5* take forever to lvl up, in the meantime I maxed two of my 4* TD, as such I swapped over 2 new low lvl ones, since I dont want to "waste the exp" on those two character slots thus I replaced those two L50 with new ones.
Its not "wasting" per say, rather its a matter of perception - why not lvl up other tanks if you can and it doesnt affect your team performance in any way ? (for hard Event maps, I will swap those two back in)