I make primarily very small baits that have a super amount of transparency in the colors and I use stabilizer if I see that I need some buffering but then I am also re-heating and re-melting these colors a bunch of times. The colors I make are also more on the light side than the darker bass bait type of colors and the stabilizer gives me some security while heating like I do. As Mike and Andy have pointed out it isn't required for injecting much of the time, however I think its a good way to help those just getting started handle the plastic until an understanding of the cooking process has been established. Stabilizer can go a long way in helping to prevent a spoiled batch due to burned plastic. It only takes a few extra seconds in a microwave or a couple extra degrees to ruin a batch, most of which comes from inexperience and the stabilizer can cushion your plastic to cover those kinds of overages. It may not be an "essential" but I'd suggest getting some until the cooking aspects get worked out.
Hand in hand with stabilizer is a good thermometer, like the digital that Do-It sells in their on-line store. Its very affordable, its easy to use and if it becomes a constant in the cooking process stabilizer can quickly be phased out and used only in certain applications where the plastic may need some help due to what's been added to it.