They do act as spacers in addition to levelers. You can get the plastic clips for 1/8 or 1/16.

In our experience they made a huge difference in the proper leveling of the tiles. We tiled the whole ground floor of the house, and the part where we only used regular spacers isn’t as even as where we used the tile leveling system (fortunately it’s just a small part, we wised up pretty quickly) the system we used is made by Peygran; we were able to reuse much of the system and just needed to repurchase the plastic clips. It’s not cheap, but the result was worth it.