If thou want a reason for not using free exp -
Always keep in mind that when you are using free experience, you are losing credits and badges ( this statement might have confused you ..... Continue reading). Let me give you an example - I have an SU 152 with me (with 15k experience more needed for ISU 152). If I use my free experience, I will be skipping a few battles (around 20?), that means I won't get any credits for those 17-20 matches and if on an average, I get a profit of 20k credits per battle, I'll be at a loss of around 20(battles) x 20k (average profit) that is 400 k credits. Instead of using my free exp, if I put in some effort, I'll end up getting more credits (which I can use to buy equipment!

), getting more free exp (for upgrades), avoiding that huge sum of 15k free exp

[and if later WG decides to give 15% off on tier 8 (this happened to me today

!!!!!), I will be saving credits ;) and in those 17-20 battles I'll also get a handful of badges

]
I did the same with my SU 100 (and later bought the equipment for my SU 152 which reduces the loading speed by 10% -a much needed for the stock gun

).
Hope this helps you!
Edited by Clash_0f_Clans, 24 November 2014 - 06:26 PM.