I did some calculations back in November for purchasing miners with and without WTT to find the break even points where i had earned back the money spent for the miner + WTT. This assumes WTT was at 1.70, and all crypto prices were calculated on 11-24-2017. But the math is still valid to show you a general idea of the benefits of buying WTT. Also, you are still being charged the discounted rate of $0.033 per kw/h while using WTT (instead of the standard ~$0.09 per kw/h) and this is factored into the monthly profit.

Miner  |  Rig Price  |  WTT (Price)  |  Hash Rate   |  Monthly Profit (No WTT) |   Monthly Profit (WTT) |  Break-Even
Antminer S9 (ASIC - BTC)   $2,100    1456 ($2,475)   13.5 TH/s   $517    $577    4 months / 8 months
Antminer L3+ (ASIC - LTC)   $2,700    880 ($1,496)   500 MH/s   $422    $458    6.4 months / 9.1 months
Alpha Miner 200 (GPU - ETH)   $3,300    1540 ($2,618)   250 MH/s   $387    $450    8.5 months / 13.1 months
Antminer D3 (ASIC - DASH)   $2,200    1210 ($2,057)   15 GH/s   $96    $145    23 months / 29 months


TLDR: Buy WTT for long term mining, you will get better returns in the long run, but short term the monthly profit difference is small.