I always have verify enabled; if you for some reason don't have time to verify one disc, you can always cancel the verification before it's finished.
Verification assures that your disc is recognizable and readable (in that drive) and that the data hasn't been somehow corrupted. 99% of the time verification will pass when using good media in good burners at a reasonable burning speed, but you don't want to be caught by surprise for the rare case when your burn is not OK - that's what verification gives you.
I burn using a Pioneer 116 and I only use TY DVD-R 8x discs
I only burn at 4x, should I burn slower or is 4x fine
You should burn faster with that drive - at least 6x, but 8x is probably just as good or even 12x.
These newer drives are not optimized (or even tested?) for burning at 4x with 8x/16x certified DVD media and the results when burning at 4x are not as good as when burning at 6x, 8x or 12x.