Goggles are necessary, at least we think so. Like every other piece of equipment some people are very passionate about them. Currently, we wear whatever we like. Roka, our swim sponsor, does not make goggles. They're currently focused on making the best swimskins and wetsuits, and they do that very well.
So, we pick and choose our goggles. And, we like having new goggles. Jumping in the pool with new unscratched lenses is great. Since both of us come from a swim background, we have worn a LOT of different styles. What we wear now that triathlons are our main gig is different than what we wore as swimmers. But, some triathletes stick to the same goggles that they wore as swimmers. In the past, we both raced and trained in the hard plastic no gasket 'Swedish' style goggles. Now, we both wear larger, soft plastic goggles with a double strap.
Neither one of us particularly like the goggles that have a buckle style adjustment on the side of each eyepiece. Amy wears her goggles OVER her swim cap during training and UNDER her cap during races. Brandon wears his goggles UNDER his swim cap, even while training. That is personal preference. Some people have had bad experiences one way or the other, so they stick with what has worked.
To wrap up, if you need goggles, go by your nearest shop...if there is one close by. And, if you are in Austin, go by Austin Tri-Cyclist as they are part of the 'Slowtwitch Goggle Tour'. The tour gives you the opportunity to try on a variety of goggles to see which might work the best for you and which might fit your face the best. Right now, our go-to goggles are the Zoggs Predators.