I'd probably take it out. It may have been added as a pressure limiter device for a valve(s) that didn't like the high pressure if the system is closed and doesn't have an expansion tank. It is a bandaid. A properly designed system shouldn't need one.
Do a search here on expansion tanks and see if you need one. If you do, then since you're changing things, you might as well do it right.
If your static pressure is too high, you should have a prv. If you have a prv and/or you have a check valve in the water supply, you also need an expansion tank. the proper place for that is on the cold side of the WH somewhere (not on the hot side where it would work, but the heat would make it fail sooner).