Is it really necessary to have an i-TTL flash for my Nikon camera?

I am a photo enthusiast and I bought a i-TTL flash (Sigma EF 610 DG ST) recently and have the option of returning it. After using it for two days, I really wonder if I ever need one. Firstly, my house is very brightly lit and I can always use some lamp to highlight my subjects. If things are a bit dark, I could crank up the ISO, use a tripod and decrease the shutter speed etc… Bounce flash is good but I really wonder if it is better to return this and use the money to get a good zoom lens as I always try to use natural lighting if possible. I have a Nikon D3200 with 18-55mm lens and 50mm prime 1.8 lens. I could use this external flash only in TTL mode, full power, 1/16th. There are no other options. I do not have full manual control. The maximum shutter speed I can set is 1/200 I guess and I can't use it in bright sunlight when my subject is having shadows on the face caused by the sun. I have to go for a reflector and I do not know if I can accomplish it with a flash. Moreover, the manual says that I have to use the flash daily in order to maintain capacitor operation. So what do you think I should do? I am confused. I don't use my DSLR everyday.

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